Invasive Plants 

and Weeds of the 

National Forests 

and Grasslands in 

the Southwestern 

Region

Second Edition

United States 

Department of 

Agriculture

Forest

Service

Southwestern 

Region

MR-R3-16-6

December 2013
The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and 

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USDA is an equal opportunity provider and employer.

Printed on recycled paper • December 2013

Cover Image: Tall morning-glory (Ipomoea 

purpurea (L.) Roth) USDA-NRCS PLANTS 

Database/USDA NRCS. “Wetland Flora: Field 

Office Illustrated Guide to Plant Species.” USDA 

Natural Resources Conservation Service. 
Invasive Plants 

and Weeds of the 

National Forests and 

Grasslands of the 

Southwestern Region

Second Edition

Compiled and Edited by

Mitchel R. White, Ph.D.

Ecologist

USDA Forest Service

Southwestern Region

Apache-Sitgreaves National Forests
To solve a problem, we must first 

understand the problem. This field 

guide is designed to help identify 

the invasive plants that threaten our 

forests and grasslands.
i

Introduction

This second edition has been compiled to include additional 

nonnative, undesirable weeds that were left out of the first edition. 

Thirty-one additional species were added to reflect the concerns of 

forest personnel throughout the Southwestern Region.

As defined in Executive Order 13112, an “invasive species” 

(including plants) means an alien species whose introduction does or 

is likely to cause economic or environmental harm or harm to human 

health. Invasive plants are nonnative plant species that can grow 

and spread rapidly, thereby replacing native plant species. Invasive 

plants generally have one or more of the following characteristics: 

aggressiveness, difficult to manage, poisonous, toxic, parasitic, 

potential carrier or host for serious insects or diseases, and are new 

or uncommon to the United States or parts thereof. The definition of 

a weed is any undesired, uncultivated plant that grows out of place 

and competes with other plants for water, nutrients, and space. 

Control of invasive plants and common weeds should be 

everyone’s concern since they can occur across all landownerships. 

Invasive plants and weeds compete with crops; poison or injure 

livestock, wildlife and people; reduce forage for wildlife and 

livestock; change natural fire regimes; and reduce recreation 

enjoyment because of thorns, allergies or unsightliness. Invasive 

plants and weeds also destroy the beauty and natural habitats of the 

Southwest wherever and whenever they occur.

Invasive plants continue to spread into uninfested areas in 

the western United States. On Federal lands, it is estimated that 

invasive plants occur on more than 17 million acres. An estimated 

6 to 7 million acres are currently infested on National Forest 

System lands, with a projected potential for increasing at a rate of 

8 to 12 percent per year. Invasive plants and common weeds infest 

native plant communities in increasing numbers throughout the 

Southwest and are beginning to appear on the national forests and 

grasslands in greater numbers every passing year. Invasive plants 
ii

have a significant environmental advantage over native plant species 

because they are free of natural enemies. Invasive plants pose an 

increasing threat to native ecosystems. This is why prevention and 

direct control methods must be used to stress or remove invasive 

plants and weeds from native plant communities.

The invasive plants listed in this document have been introduced 

to the Southwest from another place without the accompaniment of 

their natural predators or environmental controls to keep them in 

check. As a result, these plants can overwhelm native plant species 

and ecosystems, and spread dramatically year by year.

Control of invasive plant and common weed infestations 

requires the development and implementation of a management 

program, which focuses on: (1) preventing the introduction of new 

invasive plants and weeds; (2) early detection of infestations; (3) 

conducting early treatment of new infestations; and (4) containing 

and controlling established infestations at times and places that make 

them most effective and efficient. The most effective and efficient 

combination depends on factors such as the biology of the particular 

plant(s) and the circumstances under which it is growing. The overall 

priority for treatment is invasive plants over weeds, due to the greater 

threat of the former.

Because some invasive plants and common weeds pose 

challenges to land managers in dealing with the health of forests, 

woodlands, and grasslands, a series of weed management field 

guides has been published for management of invasive plant and 

common weed species in the Southwest. This book is a companion 

document intended to work in conjunction with those individual 

management field guides. The management field guides are available 

at our Forest Health Web site: http://www.fs.usda.gov/main/r3/forestgrasslandhealth/invasivespecies
iii

This book serves as the U.S. Forest Service’s guide for 

identifying invasive plants and common weeds in forests, woodlands, 

grasslands, and deserts associated with its Southwestern Region. The 

Southwestern Region (Region 3) encompasses Arizona and New 

Mexico, which together have 11 national forests (NFs). The region 

also includes four national grasslands (NGs) located in northeastern 

New Mexico, western Oklahoma, and the Texas panhandle.

National Forests and Grasslands in Region 3 by State

Arizona New Mexico Oklahoma Texas

ApacheSitgreaves NFsCarson NF Black Kettle NG Black Kettle NG

Coconino NF Cibola NF Rita Blanca NG McClellan Creek 

NG

Coronado NF Gila NF Rita Blanca NG

Kaibab NF Kiowa NG

Prescott NF Lincoln NF

Tonto NF Rita Blanca NG

Santa Fe NF
iv
v

Common Name Scientific Name Page

Grasses

Arabiangrass Schismus arabicus Nees 2

Buffelgrass Pennisetum ciliare (L.) Link 4

Cheatgrass Bromus tectorum L. 6

Crimson fountaingrass Pennisetum setaceum (Forssk.) 

Chiov.

8

Field sandbur Cenchrus spinifex Cav. 10

Giant reed Arundo donax L. 12

Japanese brome Bromus japonicus Thunb. 14

Johnsongrass Sorghum halepense (L.) Pers. 16

Jointed goatgrass Aegilops cylindrica Host 18

Lehmann lovegrass Eragrostis lehmanniana Nees 20

Mediterranean grass Schismus barbatus (loefl. ex L.) 

Thell.

22

Quackgrass Elymus repens (L.) Gould 24

Ravennagrass Saccharum ravennae (L.) L. 26

Red brome Bromus rubens L. 28

Rescuegrass Bromus catharticus Vahl 30

Ripgut brome Bromus diandrus Roth 32

Southern sandbur Cenchrus echinatus L. 34

Tall fescue Schedonorus phoenix (Scop.) Holub 36

Uruguayan pampas 

grass 

Cortaderia selloana (Schult. & 

Schult. f.) Asch. & Graebn.

38

Weeping lovegrass Eragrostis curvula (Schrad.) Nees 40

Wild oat Avena fatua L. 42

Shrubs and Trees

African sheepbush Pentzia incana (Thunb.) Kuntze 46

African sumac Rhus lancea L. f. 48

Camelthorn Alhagi maurorum Medik. 50

Himalayan blackberry Rubus armeniacus Focke 52

Contents
vi

Lilac chastetree Vitex agnus-castus L. 54

Russian olive Elaeagnus angustifolia L. 56

Saltcedar Tamarix spp. 58

Siberian elm Ulmus pumila L. 69

Sweet resinbush Euryops multifidus (Thunb.) DC 62

Tree of heaven Ailanthus altissima (Mill.) Swingle 64

Green or Inconspicuous Flowered Forbs

Common cocklebur Xanthium strumarium L. 68

Eurasian watermilfoil Myriophyllum spicatum L. 70

Halogeton Halogeton glomeratus (M. Bieb.) C. 

A. Mey

72

Kochia Bassia spp. All 74

Parrot feather milfoil Myriophyllum aquaticum (Vell.) 

Verdc.

76

Russian thistle Salsola spp. 78

Spiny cocklebur Xanthium spinosum L. 80

Pink, Rose, Red, or Purple Flowered Forbs

Alfalfa Medicago sativa L. 84

Black henbane Hyoscyamus niger L. 86

Blue mustard Chorispora tenella (Pall.) DC. 88

Bull thistle Cirsium vulgare (Savi) Ten. 90

Canada thistle Cirsium arvense (L.) Scop. 92

Common burdock Arctium minus Bernh. 94

Diffuse knapweed Centaurea diffusa Lam. 96

Hounds-tongue Cynoglossum officinale L. 98

Iberian knapweed Centaurea iberica Trevir. ex Spreng. 100

Meadow knapweed Centaurea debeauxii Gren. & Godr. 

[excluded]

102

Musk thistle Carduus nutans L. 104

Purple loosestrife Lythrum salicaria L. 106

Purple starthistle Centaurea calcitrapa L. 108
vii

Red clover Trifolium pratense L. 110

Redstem filaree Erodium cicutarium (L.) L’Hér. ex 

Aiton

112

Russian knapweed Acroptilon repens (L.) DC. 114

Scotch thistle Onopordum acanthium L. 116

Spiny plumeless thistle Carduus acanthoides L. 118

Spotted knapweed Centaurea stoebe L. 120

Squarrose knapweed Centaurea virgata Lam. 122

Tall morning-glory Ipomoea purpurea (L.) Roth 124

Teasel Dipsacus fullonum L. 126

Blue or Violet Flowered Forbs

Bigleaf periwinkle Vinca major L. 130

Carolina horsenettle Solanum carolinense L. 132

Chicory Cichorium intybus L. 134

White Flowered Forbs

African rue Peganum harmala L. 138

Broadleaved 

pepperweed

Lepidium latifolium L. 140

Field bindweed Convolvulus arvensis L. 142

Hairy whitetop Cardaria pubescens (C.A. Mey.) 

Jarmolenko

144

Horehound Marrubium vulgare L. 146

Lens-podded hoarycress Cardaria chalepensis (L.) Hand.-

Maz.

148

Onionweed Asphodelus fistulosus L. 150

Oxeye daisy Leucanthemum vulgare Lam. 152

Poison hemlock Conium maculatum L. 154

White clover Trifolium repens L. 156

White sweetclover Melilotus albus (L.) Lam. 158

Whitetop Cardaria draba (L.) Desv. 160
viii

Yellow Flowered Forbs

Black medick Medicago lupulina L. 164

Black mustard Brassica nigra (L.) W.D.J. Koch 166

Burclover Medicago polymorpha L. 168

Curveseed butterwort Ceratocephala testiculata (Crantz) 

Roth

170

Dalmatian toadflax Linaria dalmatica (L.) Mill 172

Dyer’s woad Isatis tinctoria L. 174

Floating primrosewillowLudwigia peploides (Kunth) P.H. 

Raven spp. montevidensis (Spreng.) 

P.H. Raven

176

Globe chamomile Oncosiphyon piluliferum (L. f.) 

Källersjö

178

Leafy spurge Euphorbia esula L. 180

Little hogweed Portulaca oleracea L. 182

Maltese starthistle Centaurea melitensis L. 184

Mediterranean sage Salvia aethiopis L. 186

Perennial sowthistle Sonchus arvensis L. 188

Perennial wallrocket Diplotaxis tenuifolia (L.) DC. 190

Puncturevine Tribulus terrestris L. 192

Rush skeletonweed Chondrilla juncea L. 194

Saharan mustard Brassica tournefortii Gouan 196

Sicilian starthistle Centaurea sulphurea Willd. 198

Spiny sowthistle Sonchus asper (L.) Hill 200

Tansy ragwort Senecio jacobaea L. 202

Texas blueweed Helianthus ciliaris DC. 204

Wild mustard Sinapis arvensis L. 206

Wooly mullein Verbascum thapsus L. 208

Yellow salsify Tragopogon dubius Scop. 210

Yellow starthistle Centaurea solstitialis L. 212

Yellow sweetclover Melilotus officinalis (L.) Lam. 214

Yellow toadflax Linaria vulgaris Miller 216
ix

Acknowledgements

I would like to thank all of the individuals and/or organizations 

who so graciously granted permission and allowed the use of their 

photographs; they are accredited under each individual photograph 

used in this guide. The full list of photography credits can be found 

on page 218.

I would like to acknowledge and thank Michelle W. Davalos, 

Patti Fenner, Laura Moser, Chris Nelson, Sandra Roberts, Teresa 

Smergut, Allen White, and Linda J. WhiteTrifaro for their help 

in preparation of this book. I also thank the forest and district 

employees of the Southwestern Region.
x

Arizona Noxious Weed Law and Rules. Plant Service Division. 2005. 

Prohibited, regulated and restricted noxious weeds (May 

1, 2006). Arizona Department of Agriculture. Available 

at: http://www.azda.gov/PSD/quarantine5.htm

Barkworth, M.E., K.M. Capels, S. Long, L.K. Anderton, and M.B. 

Piep (eds.). 2007. Flora of North America: North of 

Mexico Volume 24: Magnoliophyta: Commelinidae (in 

part): Poaceae, part 1. Oxford University Press, New 

York, NY.

Barkworth, M.E., K.M. Capels, S. Long, and M.B. Piep (eds.). 2003. 

Flora of North America: North of Mexico Volume 25: 

Magnoliophyta: Commelinidae (in part): Poaceae, part 2. 

Oxford University Press, New York, NY.

California Department of Food and Agriculture Division of Plant 

Health and Pest Prevention Services (PHPPS). 2010. @ 

http://www.cdfa.ca.gov/phpps

CalPhotos. CalPhotos is a project of BSCIT. University of California, 

Berkeley @ http://calphotos.berkeley.edu/. Last updated 

on 08/10/10.

Executive Order 13112. February 3, 1999. Invasive Species. Federal 

Register, Vol. 64, No. 25, Monday, February 8, 1999. 

Presidential Documents. Pp 6183-6186.

Forestry Images.org. Available at: http://www.forestryimages.org/

about/

Hilty, J. 2002-2010. Illinois wildflowers. @ http://www.

illinoiswildflowers.info/

Invasive.org, Center for Invasive Species and Ecosystem Health. 

The University of Georgia - Warnell School of Forestry 

and Natural Resources and College of Agricultural and 

Environmental Sciences - Department of Entomology @ 

http://www.invasive.org/species.cfmForestryimages Last 

updated on 07/08/10.

Kearney, T.H.; and R.H. Peebles. 1979. Arizona flora, 2nd ed. 

University of California Press, Berkeley, CA.

References
xi

McDougall, W.B. 1973. Seed plants of northern Arizona. Museum of 

Northern Arizona, Flagstaff, AZ.

New Mexico Noxious Weed Law and Rules. Office of the Director/

Secretary. 1998. New Mexico noxious weed list (October 

20, 2003). New Mexico Department of Agriculture. 

Available at: http://nmdaweb.nmsu.edu/animal-andplant-protection/noxious-weeds/weed_memo_list.pdf

Oklahoma Noxious Weed Law and Rules. Oklahoma House of 

Representatives. 1998. House Bill 2277 (October 20, 

2003). State of Oklahoma. Available at: http://www.

oklaosf.state.ok.us/~okag/forms/law/noxweedlaw.htm

SEINet (Southwest Environmental Information Network). Available 

at: http://swbiodiversity.org/seinet/index.php

Springer, J.D., M.L. Daniels, and M. Nazaire. 2009. Field guide to 

forest and mountain plants of northern Arizona. The 

Northern Arizona Ecological Restoration Institute, 

Flagstaff, AZ.

Texas Noxious Weed Law and Rules. Texas Administrative Code. 

2005. Quarantines and noxious plants, Chapter 19 (May 

24, 2006). State of Texas. Available at: http://www.

statutes.legis.state.tx.us/Docs/AG/htm/AG.78.htm

Timme, R.E. @ http://www.ruthtimme.com. Last updated on 

11/16/09 by Ruth E. Timme.

USDA, NRCS. 2010. The PLANTS Database (http://plants.usda.

gov, 11 August 2010). National Plant Data Center, Baton 

Rouge, LA 70874-4490 USA.

USDA, Forest Service. Fire effects information @ www.fs.fed.us/

database/feis/plants/index.html.

USDA, Forest Service. Forest Service Manual (FSM) 2080. Noxious 

Weed Management. USDA Forest Service, Washington, 

DC.

USDA, Forest Service. 1997. Region 3 rangeland analysis and 

management training guide. Appendix A noxious 

weeds. USDA Forest Service, Southwestern Region, 

Albuquerque, NM.
xii

USDA, Forest Service. 1999. Noxious weed management: A regional 

strategy for the protection and restoration of native 

plant communities. USDA Forest Service, Southwestern 

Region, Albuquerque, NM.

Westbrooks, R. 1998. Invasive plants, changing the landscape 

of America: Fact Book. Federal Interagency for the 

Management of Noxious Weeds and Exotic Weeds 

(FICMNEW). Washington, DC.

Whitson, T.D., L.C. Burrill, S.A. Dewey, D.W. Cudney, B.E. Nelson, 

R.D. Lee, and R. Parker. 2001. Weeds of the West, 5th 

ed. Western Society of Weeds, Grand Teton Lithography, 

Jackson, WY.

White, M.R. 2008. Field guide to noxious and invasive weeds known 

to occur or are potentially occurring on the ApacheSitgreaves National Forests. USDA Forest Service, 

Southwestern Region, MR-R3-01-2. Albuquerque, NM.

White, M.R. 2011. Invasive Plants and Weeds of the National Forests 

and Grasslands in the Southwestern Region. USDA 

Forest Service, Southwestern Region, MR-R3-16-6. 

Albuquerque, NM.
xiii

Weed Classifications

Arizona

Arizona prohibited are noxious (= regulated) weeds prohibited 

from entry into the state. This includes plants, stolons, rhizomes, 

cuttings, and seeds.

Arizona regulated are noxious weeds regulated and if found 

within the state, may be controlled or quarantined to prevent further 

infestation or contamination. This includes plants, stolons, rhizomes, 

cuttings, and seeds.

Arizona restricted are noxious weeds restricted and if found 

within the state, shall be quarantined to prevent further infestation or 

contamination. This includes plants, stolons, rhizomes, cuttings, and 

seeds.

New Mexico

New Mexico Class A species are currently not present in New 

Mexico, or have limited distribution. Preventing new infestations 

of these species and eradicating existing infestations is the highest 

priority.

New Mexico Class B species are limited to portions of the state. 

In areas with severe infestations, management should be designed to 

contain the infestation and stop any further spread.

New Mexico Class C species are widespread in the state. 

Management decisions for these species should be determined at the 

local level, based on feasibility of control and level of infestation.

New Mexico Watch List species are species of concern in the 

state. These species have the potential to become problematic. More 

data is needed to determine if these species should be listed. When 

these species are encountered, please document their location and 

contact appropriate authorities.
xiv

Oklahoma

Oklahoma noxious weeds are plants designated as noxious 

weeds by the legislature as a public nuisance in all countries across 

the state.

Texas

Texas noxious plants and invasive plants are defined as plant 

species that have serious potential to cause economic or ecological 

harm to the state.
1

Grasses

Crimson fountaingrass © F&KS
2

Arabiangrass

Schismus arabicus Nees (Grass family, Poaceae)

Description

Arabiangrass is a very short winter annual bunchgrass. It 

produces dense, low leafy growth in the fall. Spring growth starts 

earlier than most other annual grasses. It does not have creeping 

stolons or rhizomes; however, it has an extensive fibrous root system 

and tillers profusely.

Plants: Culms 3/4 to 6-3/4 inches tall; auricles absent; ligules 

of hairs less than 1/16 inch long; leaf blades 1-1/2 to 2-3/8 inches 

long, less than 1/16 inch wide, lower surfaces glabrous or sparsely 

pubescent, upper surfaces sparsely to densely pubescent.

Inflorescence/Spikelet/Floret: Flowers April to June; 

inflorescence is a dense raceme panicle, 3/8 to 1-3/8 inches long; 

spikelets 3/16 to 5/16 inch long; lower glumes 5/32 to 1/4 inch long, 

equaling or exceeding the uppermost florets; upper glumes slightly 

shorter than the lower; lemmas 1/16 to 3/32 inch long, with dense, 

spreading pubescence between the nerves, lobes longer than wide, 

acute to acuminate; paleas shorter than the lemmas.

Habitat

Cultivated and disturbed or degraded sites in desert and 

semidesert grassland communities, and roadsides within elevations 

that generally range below 4,500 feet.

Propagation/Phenology

Reproduces by seed.

Comments

Native to southwestern Asia; Arabiangrass effectively limits 

nutrients for other plants and can increase the frequency and extent 

of fire. Arabiangrass is very similar to, and difficult to tell apart from, 

Mediterranean grass. This species generally occurs as a weed in 

wildland areas of the Southwestern Region rather than as an invasive 

plant.
3

Grasses

Arabiangrass inflorescence 

© JMD

Arabiangrass florets 

© SH

Arabiangrass plant(s) 

© JMD

Arabiangrass spikelet 

© ASUH
4

Buffelgrass

Pennisetum ciliare (L.) Link (Grass family, Poaceae)

Description

Buffelgrass is an erect to decumbent, warm season, perennial 

bunchgrass that forms thick mats or tussocks with dense, geniculate 

culms, these are occasionally described as stoloniferous, 4 to 60 

inches tall; roots are thick, often long and tough, and with some 

ecotypes, rhizomatous.

Plants: Culms 4 to 60 inches, erect, sometimes branching at 

the aerial nodes, glabrous, sometimes scabrous beneath the panicle; 

nodes glabrous; leaves green or blue-green; sheaths laterally 

compressed and keeled, glabrous or pubescent, margins ciliate; 

ligules less than 1/8 inch long, membranous, ciliate; blades 1-1/8 to 

15-3/4 inches long, 1/16 to 1/2 inch wide, flat, glabrous or pubescent, 

margins ciliate or glabrous basally; often turn reddish during cooler 

weather.

Inflorescence/Spikelet/Floret: Flowers July to October; 

inflorescence is generally cylindrical in outline, 3/4 to 5-1/2 inches 

long, and can be purple, gray or yellowish; spikelets are solitary 

or clustered, and are surrounded by numerous bristles; bristles are 

separate, not fused.

Habitat

Cultivated and disturbed or degraded sites in desert and semidesert grassland communities, and roadsides within elevations that 

generally range below 4,500 feet.

Propagation/Phenology

Reproduces vegetatively and by seed.

Comments

Native to the Mediterranean region; forms dense thickets that 

displace native species, highly competitive, because it strongly 

modifies the communities it invades, and can be difficult to control; 

plants can rapidly develop colonies; contributing to the conversion of 

desert shrub communities to grassland in some areas by facilitating 

periodic fires. Arizona prohibited/regulated noxious weed.
5

Grasses

Buffelgrass inflorescence

© JMD

Buffelgrass leaf-collar region

© JMD

Buffelgrass 

plants

© JMD

Buffelgrass 

infestation

© JMR
6

Cheatgrass 

Bromus tectorum L. (Grass family, Poaceae)

Description

Cheatgrass is a tufted, cool-season annual bunchgrass; at 

maturity the foliage and seed heads often become purplish before 

drying completely and becoming brown or tan; it becomes extremely 

competitive with other grasses and displaces native species.

Plants: Cheatgrass is a tufted, cool-season annual bunchgrass 

with erect or ascending culms; characteristically reaching a height 

of 4 to 36 inches; leaf sheaths and culms are densely and softly 

retrorsely pubescent to pilose, upper sheaths sometimes glabrous; 

auricles are absent; ligule is less than 1/8 inch long, glabrous, obtuse, 

lacerate; blades are flat, less than 1/4 inch wide and up to 6-1/4 

inches long; both surfaces softly hairy. 

Inflorescence/Spikelet/Floret: Flowers May to June; 

inflorescence is open, lax, drooping, usually one-sided, 2 to 6 

inches long; nodding spikelets 4 to 8 per node, 3/8 to 3/4 inch long, 

moderately laterally compressed, usually purplish tinged, with 4 to 

8 florets; glumes are villous, pubescent, or glabrous with hyaline 

margins, awnless; lower glumes 3/16 to 5/16 inch long, 1-nerved; 

upper glumes 1/4 to 1/2 inch long, 3 to 5 nerved; lemmas 3/8 to 1/2 

inch long, lanceolate in shape, glabrous or pubescent to pilose, 5- to 

7-nerved, rounded over the midnerve, margins are hyaline, often with 

some hairs longer than those on back, tips acuminate, hyaline, teeth 

less than 1/8 inch long; awns 3/8 to 5/8 inch long, straight, arising 

below the lemma tip.

Habitat

Cultivated and disturbed or degraded sites in meadows, 

grassland, chaparral, woodland, and riparian communities, and 

roadsides within elevations that generally range below 8,500 feet.

Propagation/Phenology

Reproduces by seed; density of cheatgrass plants can range 

between 1 and 1,400 plants per square foot, and averages around 600 

plants per square foot.
7

Grasses

Comments

Native to Eurasia and Africa; cheatgrass has a compressed 

phenology and usually dries out and casts seeds by mid-June; 

these dry plants can fuel wildfires; if fires occur frequently, 

perennials will likely give way to a community dominated by 

cheatgrass and other annuals. New Mexico Class C noxious 

weed.

Cheatgrass inflorescence 

© SD

Cheatgrass leaf-collar region 

(left)

© SD

Cheatgrass inflorescences 

© CE

Cheatgrass plants

© CE
8

Crimson Fountaingrass

Pennisetum setaceum (Forssk.) Chiov. (Grass family, Poaceae)

Description

Crimson fountaingrass is a very showy warm-season perennial 

bunchgrass with graceful, arching leaves, and erect or nodding rosecolored panicles; roots fibrous, without rhizomes.

Plants: Culms 4 to 60 inches, erect, pubescent beneath the 

panicle; nodes glabrous; leaves green, sometimes bluish-green; 

sheaths glabrous, margins ciliate with white hairs; ligules less than 

1/8 inch long; blades 7-7/8 to 25-1/2 inches long, less than 1/8 inch 

wide, rolled or folded, scabrous, midveins noticeably thickened.

Inflorescence/Spikelet/Floret: Flowers June to October; 

inflorescence is generally cylindrical in outline, 2-3/8 to 12-1/2 

inches long and 1-9/16 to 2-1/16 inches wide, erect or arching, 

pink to dark burgundy; spikelets are solitary or clustered, and are 

surrounded by numerous bristles; bristles are separate, not fused.

Habitat

Cultivated and disturbed or degraded sites in desert and semidesert grassland communities, and roadsides within elevations that 

generally range below 4,500 feet.

Propagation/Phenology

Reproduces by seed.

Comments

Native to the Mediterranean region; contributing to the 

conversion of desert shrub communities to grassland in some areas 

by facilitating periodic fires. New Mexico Watch List species.
9

Grasses

Crimson fountaingrass 

inflorescence

© F&KS

Crimson 

fountaingrass 

leaf-collar region 

(right)

© RO

Crimson fountaingrass plants

© F&KS

Crimson 

fountaingrass 

infestation

© JMR
10

Field Sandbur 

Cenchrus spinifex Cav. (Grass family, Poaceae)

Description

Warm-season tufted annual or short-lived perennial grass arising 

from a geniculate base; roots are fibrous, shallow, occasionally rooting 

at the nodes, from 12 to 40 inches tall; with loose spikes of spiny burs 

at maturity.

Plants: Loosely tufted; culms branched and often abruptly bent 

near the base; leaf sheaths flattened, glabrous or sparsely pilose; blades 

flat, sometimes folded, appear glabrous, but are rough with very short 

hairs; blades 1/8 to 5/16 inch wide and 1-1/8 to 11 inches long, either 

flat or folded; glabrous or sparsely covered with long, soft hairs; 

ligules less than 1/16 inch long. 

Inflorescence/Spikelet/Floret: Flowers July to September; 

inflorescences terminal, spike-like panicles of burs, 1 to 3-1/4 

inches long; burs 3/16 to 3/8 inch long and less than 3/16 inch wide, 

consisting of 1 to 2 series of many stiff, partially fused, sharp bristles 

surrounding 2 to 4 spikelets; outer bristles, when present, mostly 

flattened; inner bristles 8 to 40, less than 3/16 inch long and less than 

1/16 inch wide, fused at least half their length; disarticulation at the 

base of the burs; spikelets 2 to 4 per bur, 1/8 to 1/4 inch long, glabrous; 

lower glumes less than 1/8 inch long; upper glumes 3/16 inch long, 5- 

to 7-nerved; lower lemmas less than 1⁄4 inch long, 5- to 7-nerved; upper 

lemmas also less than 1/4 inch long, obscurely nerved.

Habitat

Cultivated and disturbed or degraded sandy or gravelly sites within 

elevations that generally range from 3,500 to 5,000 feet.

Propagation/Phenology

Reproduces by seed; seedlings emerge in spring or early summer, 

and growth is rapid under moist conditions.

Comments

Native to the southern United States, Mexico, Central, and 

South America; coastal sandbur is an aggressive colonizer. Arizona 

prohibited/regulated noxious weed. 
11

Grasses

Field sandbur inflorescence

© RO

Field sandbur leaf-collar region

© JMD

Field sandbur seed 

bur (left)

© RO

Field 

sandbur 

plants 

(right)

© RO
12

Giant Reed 

Arundo donax L. (Grass family, Poaceae)

Description

Giant reed is a tall, bamboo-like, perennial grass that can grow to 

over 30 feet in height; fleshy, creeping rhizomes, up to 3/8 inch thick, 

form compact masses from which tough, fibrous roots emerge that 

penetrate deeply into the soil.

Plants: Culms 9-1/2 to 33 feet tall, in large tussocks or hedges; 

leaves arranged in two vertical rows on opposite sides of the culms, 

the leaves look like those of corn; ligules very short, less than 1/16 

inch long; blades 1 to 3-1/2 feet long, 3/4 to 3-1/2 inches wide, with 

a wedge-shaped, light to dark brown area at the base.

Inflorescence/Spikelet/Floret: Flowers May to October; 

panicles are plume-like, 12 to 24 inches long, to 12 inches wide; 

silver, cream, brown to purplish in color; spikelets 3/8 to 5/8 inch, 

laterally flattened, with 2 to 4 florets per spikelet; glumes nearly 

equal, as long as the spikelets, thin, brownish or purplish, 3-nerved, 

long-acuminate; lemmas 5/16 to 1/2 inch long, 3- to 5-nerved, pilose, 

hairs 4 to 9 mm, tips 2-toothed, midnerve ending into a delicate awn.

Habitat

Established in moist places such as ditches, stream and 

riverbanks, and flood plains, growing best in well drained soils where 

abundant moisture is available; tolerates a wide variety of conditions, 

including high salinity, and can flourish in many soil types from 

heavy clays to sands within elevations that generally range below 

4,000 feet.

Propagation/Phenology

Reproduces primarily by fast-growing rhizomes that produce 

new plants; giant reed can float miles downstream where root 

and stem fragments may take root and initiate new infestations, 

sometimes covering several acres. 

Comments

Native to the Mediterranean region; giant reed grows rapidly, is 

highly competitive, and can be difficult to control; plants can rapidly 

develop dense colonies. New Mexico Watch List species and Texas 

noxious plant.
13

Grasses

Giant reed inflorescences

© DJM

Giant reed leaf-collar 

region (left)

© CE

Giant reed plants

© JHM

Giant reed 

infestation 

consisting 

of young 

plants

© DJM
14

Japanese Brome

Bromus japonicus Thunb. (Grass family, Poaceae)

Description

Japanese brome is a winter annual bunchgrass. It produces dense, 

low leafy growth in the fall. Spring growth starts earlier than most 

other annual grasses. It does not have creeping stolons or rhizomes; 

however, it has an extensive fibrous root system and tillers profusely.

Plants: Culms 8-5/8 to 43-3/8 inches tall, solitary, erect or 

geniculate, slender, weak; leaf sheaths densely shaggy-pilose, 

auricles absent; ligules less than 1/8 inch long, hairy, obtuse, erose; 

leaf blades 4 to 8 inches long, 1/8 to 1/4 inch wide, coarsely pilose on 

both surfaces. 

Inflorescence/Spikelet/Floret: Flowers April to June; 

inflorescence is a panicle, 2 to 9 inches long, 1 to 4-3/4 inches wide, 

open, nodding; branches spreading to ascending, lower branches 

slightly drooping; spikelets 3/8 to 3/4 inch long, shorter than at 

least some panicle branches, ovoid-lanceolate or ovate, laterally 

compressed; florets 4 to 10, ascending spreading after flowering; 

glumes scabrous or glabrous; lower glumes 3/16 to 1/4 inch long, 3 

to 5 veined; upper glumes 1/4 to 5/16 inch long, 7 veined; lemmas 

1/4 to 7/16 inch long, less than 1/8 inch wide, elliptic, coriaceous, 

obscurely 7 veined, rounded over the midvein; awns 1/8 to 3/8 inch 

long, straight or flexuous, arising less than 1/16 inch below the 

lemma apices.

Habitat

Cultivated and disturbed or degraded sites in semidesert 

grassland and woodland communities, and roadsides within 

elevations that generally range from 4,500 to 7,200 feet.

Propagation/Phenology

Reproduces by seed. Japanese brome produces roughly 250,000 

seeds per pound.

Comments

Native to southern and south-central Europe and Asia; Japanese 

brome is an excellent seed producer and can maintain itself as a 
15

Grasses

reseeding annual; forms dense thickets that displace native 

species, highly competitive. Bromes are known to cause hay 

fever and asthma. Japanese brome has poor forage quality. 

This species generally occurs as a weed in wildland areas of 

the Southwestern Region rather than as an invasive plant.

Japanese brome inflorescence

© JMD

Japanese brome leaf collar region

© JMD

Japanese brome spikelets

© JMD

Japanese brome spikelets

© JCS
16

Johnsongrass

Sorghum halepense (L.) Pers. (Grass family, Poaceae)

Description

Johnsongrass is a large, coarse, introduced, warm-season, perennial 

bunchgrass growing to 6-1/2 feet in height, with reddish to purplishblack panicles; plant produces vigorous rhizomes.

Plants: Seedlings resemble young corn seedlings; mature plants 

typically tufted, culms 1-3/4 to 6-1/2 feet tall and 1/8 to 3/4 inch thick; 

nodes appressed pubescent; internodes glabrous; collars broad, whitish or 

pale green, smooth; auricles lacking; sheaths open, ribbed, compressed, 

glabrous or sparsely hairy near blade junction, shorter than internodes, 

pale green to reddish; ligules l-1/6 to 1/4 inches long, membranous, 

conspicuously ciliate; leaf blades, flat, 4 to 35-1/2 inches long and 3/8 to 

1-9/16 inches wide.

Inflorescence/Spikelet/Floret: Flowers May to October; panicles 

4 to 16 inches long, 2 to 10 inches wide, primary branches compound, 

terminating in groups of 1 to 5 spikelet pairs; disarticulation usually 

beneath the sessile spikelets, sometimes also beneath the pedicelled 

spikelets; sessile spikelets 3/16 to 1/2 inch long and less than 1/8 

inch wide; calluses blunt; glumes hard, shiny, appressed pubescent; 

upper lemmas unawned, or with a geniculate, twisted awn to 1/2 inch; 

pedicelled spikelets, 1/8 to 1/4 inch long; glumes membranous to 

leathery, unawned; each fertilized sessile spikelet produces a single grain.

Habitat

Cultivated and disturbed or degraded moist sites in meadow, 

grassland, and woodland communities, and roadsides within elevations 

that generally range below 8,000 feet.

Propagation/Phenology

Reproduces primarily by fast-growing rhizomes that produce new 

plants; one plant can produce up to 295 feet of rhizomes in a single 

season.

Comments

Native to the Mediterranean region; Johnsongrass grows rapidly, 

is highly competitive, and can be difficult to control; plants can rapidly 

develop colonies.This species generally occurs as a weed in wildland 

areas of the Southwestern Region rather than as an invasive plant.
17

Grasses

Johnsongrass 

plants (right)

© CTB

Johnsongrass leaf-collar region

© OSWL

Johnsongrass spikelets

© BR

Johnsongrass inflorescence

© JC
18

Jointed Goatgrass

Aegilops cylindrica Host (Grass family, Poaceae)

Description

Mostly erect, winter (cool-season) annual grass closely related 

to and resembling winter wheat, 5-1/2 to 19-1/2 inches tall, with a 

tufted appearance; roots are fibrous; reproduces by seed.

Plants: Culms erect, branching at the base, spreading, or 

abruptly bent near the base; blades flat, 1-1/8 to 6 inches long 

and about 1/16 to 3/16 inch wide; lower surface and sometimes 

upper surface sparsely covered with fine hairs; sheaths open; ligule 

membranous, less than 1/16 inch long, with the upper margins finely 

fringed; auricles about 1/16 inch long, ciliate, with hairs less than 1/8 

inch long.

Inflorescence/Spikelet/Floret: Flowers May to June; 

inflorescence is a narrow, cylindrical spike 7/8 to 4-3/4 inches long, 

disperses as a unit at maturity, but ultimately breaks apart into joints; 

joints cylindrical, with blunt ends; spikelets 1 per node, 3/8 to 1/2 

inch long, alternate, laying flat against and fitting into a groove in 

a zig-zag rachis; 2 to 5 florets/spikelet, the lower 2 usually fertile; 

glumes 1/4 to 3/8 inch long, mostly 6 to 9 nerves, awned, awns of 

lower glumes acute or tapered, less than 3/4 inch long, awns of upper 

glumes 1-3/16 to 3-1/8 inches long; lemmas about 3/8 inch long, 5 

to 7 nerves, awns of lower lemmas about 3/4 inch long, awns of the 

upper lemmas 1-3/16 to 2-3/4 inches long; awns of both glume and 

lemma awns are flanked by two teeth as well as being stiff, sharp, 

and minutely barbed; caryopses about 1/4 inch long, oblong, reddish 

to light brown, grooved, with short hairs at the apex, and adhering to 

the lemma and palea. 

Habitat

Cultivated and disturbed or degraded dry sites in grassland 

and woodland communities, and roadsides within elevations that 

generally range from 5,300 to 7,000 feet.

Propagation/Phenology

Reproduces by seed; one plant produces about 130 seeds, but 

isolated plants can produce as many as 3,000 seeds; some seeds can 

remain dormant for 2 or more years.
19

Grasses

Comments

Native to the Mediterranean region and central Asia; 

jointed goatgrass can hybridize with winter wheat. Arizona 

prohibited/restricted noxious weed and New Mexico Class C 

noxious weed.

Jointed goatgrass inflorescences (above)

© SD

Jointed goatgrass leafcollar region (above)

© SD

Jointed 

goatgrass seeds 

(right)

©SD

Jointed goatgrass 

inflorescences (right) 

compared to wheat 

inflorescences (left) 

© USDA 1
20

Lehmann Lovegrass

Eragrostis lehmanniana Nees (Grass family, Poaceae)

Description

Lehmann lovegrass is an introduced, warm-season, perennial 

bunchgrass growing from 18 to 24 inches in height; its bunch habit is 

somewhat open in that individuals do not form a compact crown with 

numerous stem bases; furthermore, although more or less erect, some 

stems are procumbent and these often root at the nodes; this often 

results in somewhat continuous stands where individuals are difficult 

to identify.

Plants: Erect culms erect, commonly geniculate, sometimes 

rooting at the lower nodes, glabrous; leaf sheaths sometimes shortly 

silky pilose near the bottom, hairs less than 1/16 inch long, sparsely 

hairy near the top, hairs less than 1/8 inch long; ligules very short, 

ciliate; leaf blades 3/4 to 4-5/8 inches long, less than 1/8 inch wide, 

flat to rolled inward, glabrous.

Inflorescence/Spikelet/Floret: Flowers July to October; 

inflorescence an open panicle, 2-3/4 to 7 inches long, 3/4 to 3-1/8 

inches wide, oblong, open; primary branches 3/8 to 3-1/8 inches 

long, appressed or diverging; spikelets 3/16 to 9/16 inch long, less 

than 1/16 inch wide, linear-lanceolate, leaden to straw-colored, with 

4 to 14 florets; glumes oblong to lanceolate, membranous; both lower 

and upper glumes less than or equal to 1/8 inch long; lemmas also 

less than 1/8 inch long, ovate, membranous, with an acute to obtuse 

tip, awnless, lateral nerves are inconspicuous.

Habitat

Cultivated and disturbed or degraded sites on sandy flats and 

on calcareous slopes in desert grassland, semidesert grassland, 

and woodland communities, and roadsides within elevations that 

generally range from 3,500 to 4,000 feet.

Propagation/Phenology

Reproduces by seed; prolific and early seed production 

is common in Lehmann lovegrass stands; it is also weakly 

stoloniferous.
21

Grasses

Comments

Native to southern Africa; if Lehmann lovegrass 

stands occur near burned sites, there is high potential for 

establishment; it is a strong competitor, especially after 

disturbance, this species can exclude native recovery; in 

addition, it is more flammable and fire tolerant than many native 

species, altering fire frequency and intensity in invaded systems. 

This species generally occurs as a weed in wildland areas of the 

Southwestern Region rather than as an invasive plant.

Lehmann lovegrass 

inflorescences

© JMD

Lehmann lovegrass spikelets

© JMD

Lehmann lovegrass leafcollar region (below)

© JMD

Lehmann lovegrass infestation

© JMR
22

Mediterranean Grass

Schismus barbatus (Loefl. ex L.) Thell. (Grass family, Poaceae)

Description

Mediterranean grass is a very short winter annual bunchgrass. 

It produces dense, low, leafy growth in the fall. Spring growth starts 

earlier than most other annual grasses. It does not have creeping 

stolons or rhizomes; however, it has an extensive fibrous root system 

and tillers profusely.

Plants: Weak culms 1/2 to 10-5/8 inches tall; auricles absent; 

ligules of hairs less than 1/16 inch long; leaf blades 1-3/16 to 5-7/8 

inches long, less than 1/16 inch wide, lower surfaces glabrous or 

scabrous, upper surfaces scabrous, sparsely long pubescent near the 

ligules.

Inflorescence/Spikelet/Floret: Flowers April to June; 

inflorescence is a dense raceme panicle, 3/8 to 3 inches long; 

spikelets 5/32 to 5/16 inch long; lower glumes 5/32 to 1/4 inch long, 

exceeded by the uppermost florets; upper glumes slightly shorter 

than the lower; lemmas 1/16 to 3/32 inch long, with appressed 

pubescence between the nerves, or glabrous and with spreading hairs 

on the margins, lobes as wide as or wider than long, acute to obtuse; 

paleas of the lower florets in the spikelets as long as or longer than 

the lemmas.

Habitat

Cultivated and disturbed or degraded sites in desert and 

semidesert grassland communities and roadsides within elevations 

that generally range below 5,000 feet.

Propagation/Phenology

Reproduces by seed.

Comments

Native to Eurasia; spikelet morphology is used to separate S. 

arabicus and S. barbatus. In S. arabicus the apical lobes of the 

lemma gradually taper to sharp, narrow points and are 30 to 50 

percent of the lemmas’ total length, whereas in S. barbatus the lobes 

are wider and have broadly pointed to rounded points that are 15 

to 25 percent of the lemmas’ total length. In S. arabicus the palea 
23

Grasses

does not generally extend beyond the base of the opening on 

the lemma, whereas in S. barbatus the palea extends beyond 

the base of the opening and may be as long as the lemma 

lobes. The length of the glumes in the terminal spikelet of the 

inflorescence is generally less than 1/4 inch in S. arabicus and 

greater than 1/4 inch in S. barbatus. This species generally 

occurs as a weed in wildland areas of the Southwestern Region 

rather than as an invasive plant.

Mediterranean grass inflorescences 

© RO

Mediterranean grass florets

© SH

Mediterranean grass leaf collar region

© JMD

Mediterranean grass plant(s)

© JMD
24

Quackgrass

Elymus repens (L.) Gould (Grass family, Poaceae)

Description

Quackgrass is an erect, sometimes tufted cool-season perennial 

to 47-1/4 inches tall, with extensive yellowish rhizomes.

Plants: Culms 12 to 47-1/4 inches tall; leaves sometimes 

somewhat basally concentrated; leaf sheaths pilose or glabrous at or 

near point of attachment; both auricles and ligule less than 1/32 inch 

long; leaf blades 1/4 to 3/8 inch wide, usually flat, lower surfaces 

glabrous or sparsely pilose, upper surfaces usually sparsely pilose 

over the veins, sometimes glabrous, veins smooth, widely spaced, 

primary veins prominent, separated by the secondary veins.

Inflorescence/Spikelet/Floret: Flowers May to September; 

inflorescence is a spike, 2 to 8 inches long, less than 3/8 inch wide, 

usually with 1 spikelet per node; spikelets 3/8 to 1-1/16 inches 

long, appressed to ascending, with 4 to 7 florets; disarticulation 

usually below the glumes, the spikelets falling intact; glumes 

oblong, glabrous, keeled distally, keels inconspicuous and smooth 

proximally, scabrous and conspicuous distally, lateral nerves 

inconspicuous, hyaline margins present in the upper half, apices 

acute, unawned or awned to 1/8 inch; lower glumes 5/16 to 7/16 

inch long, 3 to 6 nerved; upper glumes 9/32 to 15/32 inch long, 5 to 

7 nerved; lemmas 5/16 to 15/32 inch long, glabrous, mostly smooth, 

unawned or with a straight awn less than 3/8 inch long; paleas 9/32 

to 3/8 inch long, keels ciliate from half to almost the entire length, 

apices emarginate, truncate, or rounded.

Habitat

Disturbed or degraded sites in grasslands, woodlands, and forest 

communities, and roadsides within elevations that generally range 

from 6,700 to 8,500 feet.

Propagation/Phenology

Reproduces vegetatively from rhizomes and by seed; rhizomes 

tolerate considerable desiccation.
25

Grasses

Quackgrass inflorescence

© OSWL

Quackgrass leaf collar region

© SD

Quackgrass plants and rhizomes

© SD

Quackgrass plant(s)

© SD

Comments

Native to Eurasia; quackgrass is highly competitive and 

very drought tolerant; seeds can remain viable up to 4 years. 

Seedlings can emerge from soil depths of up to 4 inches; 

Arizona restricted noxious weed and New Mexico Watch List 

species.
26

Ravennagrass

Saccharum ravennae (L.) L. (Grass family, Poaceae)

Description

Ravennagrass is a tall, erect, warm-season, perennial, clumpforming grass, 9 to 13 feet tall and 4 to 6 feet wide, from a network 

of rhizomes; long blades extend up and arch from the center, with 

bamboo-like flowering canes emerging from the center.

Plants: Culms 6-1/2 to 13 feet tall, culms, nodes and sheaths 

glabrous; auricles absent; ligules less than 1/16 inch long; gray-green 

blades 19-1/2 to 60 inches long, 3/16 to 1 inch wide, glabrous, with a 

single white stripe down the middle of each.

Inflorescence/Spikelet/Floret: Flowers September to October; 

inflorescence is a plume-like panicle of spikelets covered in white or 

pale-colored silky hairs; supporting stalks 15-3/4 to 31-1/2 inches long, 

glabrous; panicles lanceolate, main axis 11-7/8 to 27-9/16 inches long, 

glabrous; primary branches 2-3/8 to 7-7/8 inches long, appressed or 

spreading; branch internodes less than 1/16 inch long; straw-colored 

sessile spikelets 1/4 inch long or less, and less than 1/16 inch wide; 

white callus hairs 1/4 inch long or less; lower glumes smooth, 4- to 

5-nerved; upper glumes 3-nerved; lower lemmas less than 3/16 inch 

long, 1-nerved; upper lemmas subequal to the lower lemmas, without 

nerves, entire; awns less than 3/16 inch long, flat, straight or curved at 

the base; pedicellate spikelets similar to sessile spikelets.

Habitat

Established in moist places such as ditches, stream and riverbanks, 

and flood plains, growing best in well drained soils where abundant 

moisture is available; within elevations that generally range below 

7,000 feet.

Propagation/Phenology

It reproduces through copious production of seed and from a 

network of rhizomes. 

Comments

Native to the Mediterranean region; ravennagrass grows rapidly, is 

highly competitive, and can be difficult to control; more cold tolerant 

than giant reed, crimson fountaingrass, or Uruguayan pampas grass. 

New Mexico Class A noxious weed.
27

Grasses

Ravennagrass inflorescence

© JMD

Ravennagrass leaf collar region

© JMD

Ravennagrass plants

© JMD

Ravennagrass young plants

© JMD
28

Red Brome

Bromus rubens L. (Grass family, Poaceae)

Description

Red brome is a tufted, cool-season, annual bunchgrass commonly 

found growing on shallow dry soil or poor textured, clayey soil; it 

becomes extremely competitive with other grasses and displaces native 

species.

Plants: Red brome is a tufted, cool-season, annual bunchgrass with 

erect or ascending culms; characteristically reaching a height of 4 to 28 

inches; leaf sheaths and culms are softly pubescent to pilose; auricles are 

absent; ligule is less than 1/8 inch long, pubescent, obtuse, lacerate; blades 

are flat, less than 3/16 inch wide and up to 6 inches long. 

Inflorescence/Spikelet/Floret: Flowers March to May; inflorescence 

is an erect, dense panicle with a purplish to reddish-brown tinge, 3/4 to 4 

inches long and 3/4 to 2 inches wide; spikelets 1 to 2 per node, 11/16 to 

1 inch long, densely crowded, moderately laterally compressed, with 4 to 

8 florets; glumes are pilose with hyaline margins, awnless; lower glumes 

3/16 to 5/16 inch long, 1- to 3-nerved; upper glumes 5/16 to 1/2 inch long, 

3- to 5-nerved; lemmas 3/8 to 5/8 inch long, linear-lanceolate in shape, 

pubescent to pilose, 7-nerved, rounded over the midnerve, margins are 

hyaline, tips acuminate, teeth less than 1/8 inch long; awns 5/16 to 13/16 

inch long, straight, reddish, arising below the lemma tip.

Habitat

Cultivated and disturbed or degraded sites in meadows, grassland, 

chaparral, woodland, and riparian communities, and roadsides within 

elevations that generally range below 7,200 feet.

Propagation/Phenology

Reproduces by seed with an average of 76 seeds per plant in natural 

populations; unlike native annuals, red brome does not produce dormant 

seed and does not maintain a soil seed bank.

Comments

Native to southern and southwestern Europe; red brome initiation and 

establishment are a direct response to fall rains; initial growth is relatively 

slow, followed by a rapid increase in vegetative growth coinciding with 

warming spring temperatures. This species generally occurs as a weed 

in wildland areas of the Southwestern Region rather than as an invasive 

plant.
29

Grasses

Red brome mature 

inflorescence

© JMR

Red brome immature inflorescence

© JMR

Red brome 

plants (right)

© JMR

Red brome 

infestation 

(left)

© JMR
30

Rescuegrass

Bromus catharticus Vahl (Grass family, Poaceae)

Description

Rescuegrass is a loosely cespitose or tufted cool-season annual, 

biennial, or perennial bunchgrass. In areas that have hot, dry 

summers and severe winter temperatures, it grows as an annual. 

It does not have creeping stolons or rhizomes; however, it has an 

extensive fibrous root system and tillers profusely.

Plants: Culms 19-1/2 to 47 inches tall, stout, solitary, erect, or 

geniculately ascending; leaf sheaths glabrous or densely pubescent; 

auricle absent; ligules less than 1/8 inch long, glabrous or pilose, 

obtuse, lacerate to erose; blades up to 1-1/2 to 12 inches long and 1/8 

to 3/8 inch wide, flat, glabrous, or hairy on both surfaces.

Inflorescence/Spikelet/Floret: Flowers March to June; 

panicles 3-1/2 to 11 inches long, usually open, erect, or nodding; 

lower branches shorter than 4 inches, 1 to 4 per node, spreading or 

ascending, with up to 5 spikelets variously distributed; spikelets 5/8 

to 1-1/2 inches long, shorter than at least some panicle branches, 

elliptic to lanceolate, strongly laterally compressed, not crowded 

or overlapping, with 4 to 12 florets; glumes smooth or scabrous, 

glabrous or pubescent, lower 1/4 to 1/2 inch long, 5 to 9 nerves, 

upper 5/16 to 5/8 inch long, 7 to 11 nerves, shorter than the 

lowest lemma; lemmas 7/16 to 3/4 inch long, lanceolate, laterally 

compressed, strongly keeled, usually glabrous, sometimes pubescent, 

smooth or scabrous, 9 to 13 nerves, nerves often raised and riblike, 

margins sometimes conspicuous, hyaline, whitish or partly purplish, 

apices entire or toothed, teeth acute, shorter than 1/16 inch; awns 

absent or to 3/8 inch.

Habitat

Cultivated and disturbed or degraded sites in desert and 

semidesert grassland communities, and roadsides within elevations 

that generally range below 4,500 feet.

Propagation/Phenology

Reproduces by seed.
31

Grasses

Comments

Native to South America; rescuegrass has been widely 

introduced into the southern half of the U.S. as a forage crop. 

Rescuegrass is able to survive in a variety of different habitats 

and can tolerate cold temperatures and drought conditions. 

These characteristics make it difficult to manage. Rescuegrass 

has excellent forage quality. This species generally occurs as a 

weed in wildland areas of the Southwestern Region rather than 

as an invasive plant.

Rescuegrass leaf collar region

© JMD

Rescuegrass plant(s) (left)

© F&KS

Rescuegrass spikelets

© F&KS

Rescuegrass inflorescence

© PA
32

Ripgut Brome

Bromus diandrus Roth (Grass family, Poaceae)

Description

Ripgut brome is a loosely cespitose or tufted annual cool-season 

bunchgrass. It produces dense, low, leafy growth in the fall. It does not 

have creeping stolons or rhizomes; however, it has an extensive fibrous 

root system and tillers profusely.

Plants: Culms 7-7/8 to 35-3/8 inches tall, erect or decumbent, 

puberulent below the panicle; leaf sheaths softly pilose, often with 

retrorse or spreading hairs; auricles absent; ligules less than 1/8 inch 

long, obtuse, lacerate or erose; blades 1-3/8 to 14-3/4 inches long, less 

than 3/8 inches wide, both surfaces pilose.

Inflorescence/Spikelet/Floret: Flowers April to June; 

inflorescence is a panicle, 5-1/8 to 14-3/4 inches long, 3/8 to 4-3/4 

inches wide, erect to spreading; panicle branches 3/8 to 2-3/4 inches 

long, stiffly erect to ascending or spreading, with 1 or 2 spikelets; 

spikelets 1 to 2-3/4 inches long, sides parallel or diverging from 

the center, moderately laterally compressed, with 4 to 11 florets per 

spikelet; glumes smooth or scabrous, margins hyaline, lower 3/4 to 

1-3/8 inches long, 1 to 3 nerves, upper 3/4 to 1-3/8 inches long, 3 to 5 

nerves; lemmas 3/4 to 1-3/8 inches long, linear-lanceolate, scabrous, 

7 nerved, rounded over the mid-nerve, margins hyaline, apices bifid, 

acuminate, teeth less than 3/16 inch long; awns 1-3/16 to 2-9/16 inches 

long, straight, arising less than 1/16 inch below the lemma apices.

Habitat

Cultivated and disturbed or degraded sites in desert and semidesert 

grassland communities, and roadsides within elevations that generally 

range from 3,200 to 4,600 feet.

Propagation/Phenology

Reproduces by seed.

Comments

Native to southern and western Europe; the common name “ripgut 

brome” suggests possible damage to animals if they consume the 

sharp, long-awned florets of this species. Ripgut brome may suppress 

the growth of native plants. Bromes are known to cause hay fever 
33

Grasses

and asthma. Ripgut brome has poor forage quality. This 

species generally occurs as a weed in wildland areas of the 

Southwestern Region rather than as an invasive plant.

Ripgut brome spikelets

© F&KS

Ripgut brome leaf collar region

© JMD

Ripgut brome spikelet

© JMD

Ripgut brome plant(s)

© F&KS
34

Southern Sandbur

Cenchrus echinatus L. (Grass family, Poaceae)

Description

Warm-season, tufted, annual grass arising from a geniculate 

base; roots are fibrous, shallow, occasionally rooting at the nodes, 

from 7-1/2 to 40 inches tall; with loose spikes of spiny burs at 

maturity.

Plants: Loosely tufted; culms branched, often abruptly bent 

near base; leaf sheaths open, flattened, glabrous, margins narrowly 

membranous, sometimes lined with a few long hairs; collar narrow, 

lighter in color; blades flat, sometimes folded, appear glabrous, but 

are rough with very short hairs; blades 1/8 to 3/8 inch wide and 2-3/8 

to 7-7/8 inches long; upper surfaces of blade bases often sparsely 

covered with long, soft hairs; ligules consist of a fringe of hairs less 

than 1/16 inch long; often there is a tuft of hairs; lower stems often 

maroon at maturity. 

Inflorescence/Spikelet/Floret: Flowers July to September; 

inflorescences terminal, spike-like panicles of highly reduced 

branches termed fascicles (burs), 1 to 4-3/4 inches long; burs 3/16 

to 3/8 inch long and less than 1/4 inch wide, consisting of 1 to 2 

series of many stiff, partially fused, sharp bristles surrounding 1 to 

4 spikelets; outer bristles 10 to 20, if present, in 1 or more whorls, 

round or flattened, less than 1/8 inch long; inner bristles usually 

strongly flattened, fused at least at the base and forming a disk, 

frequently to more than half their length; disarticulation at the base of 

the burs; spikelets 2 to 3 per bur, 3/16 to 1/4 inch long, sessile, with 

2 florets; lower florets usually sterile; upper florets bisexual; lower 

glumes ovate, scabrous, glabrous, 1-nerved, acute to acuminate, 

less than 1/8 inch long; upper glumes 3/16 to 1/4 inch long, 3- to 

7-nerved; lower and upper lemmas ovate, less than 1/4 inch long, 

obscurely nerved, acuminate.

Habitat

Cultivated and disturbed or degraded sandy or gravelly sites 

within elevations that generally range from 3,500 to 4,500 feet.

Propagation/Phenology

Reproduces by seed; seedlings emerge in spring or early summer, 

and growth is rapid under moist conditions.
35

Grasses

Comments

Native to the southern United States, Mexico, Central and 

South America; southern sandbur is an aggressive colonizer. 

This species generally occurs as a weed in wildland areas of 

the Southwestern Region rather than as an invasive plant.

Arizona prohibited/regulated noxious weed. 

Southern sandbur inflorescence

© F&KS

Southern sandbur seed bur 

© RO

Southern sandbur fiborous roots 

(below)

© RO

Southern 

sandbur 

plants (above)

© F&KS
36

Tall Fescue

Schedonorus phoenix (Scop.) Holub (Grass family, Poaceae)

Description

Tall fescue is a robust, cool-season perennial, comparatively deep 

rooted bunchgrass with short rhizomes.

Plants: Culms are hollow, erect, 20 to 80 inches tall; leaves 

convolute in young shoots; auricles ciliate, having at least 1 or 2 hairs 

along the margins; ligules less than 1/16 inch long; leaf blades 4-3/8 to 

12 inches long, 5/32 inch wide.

Inflorescence/Spikelet/Floret: Flowers May to August; 

inflorescence is a panicle, 4 to 14 inches long, branches at the lowest 

node usually 2, shorter branch with 1 to 13 spikelets, longer branch with 

3 to 19 spikelets; spikelets 5/16 to 5/8 inch long, 3/32 to 1/8 inch wide, 

3 to 9 florets; lower glumes 1/8 to 7/32 inch long; upper glumes 3/16 

to 3/8 inch long; lemmas 5/32 to 7/16 inch long, usually scabrous or 

covered with stiff, short hairs, at least near the end, rarely smooth, awns 

absent or to 5/32 inch long, terminal or attached up to just below the 

apices; paleas slightly shorter than to slightly longer than the lemmas.

Habitat

It occurs in grazed woods, along roads, ditches, and railroad tracks, 

in fallow and abandoned fields, meadows, and marshes. It is a weed of 

cultivated areas and is found in moist, disturbed places within elevations 

that generally range from 4,000 to 9,000 feet.

Propagation/Phenology

Reproduces by seed and increases vegetatively; spreads primarily 

by seed to form dense, solid stands. Tall fescue can produce roughly 

206,000 seeds per pound.

Comments

Native to Europe and central Asia; tall fescue is a long lived, 

aggressive perennial. Tall fescue’s competitive ability and persistence is 

increased by the allelopathic compounds it produces and may become 

weedy or invasive in some regions or habitats and can displace desirable 

vegetation. This species generally occurs as a weed in wildland areas of 

the Southwestern Region rather than as an invasive plant.
37

Grasses

Tall fescue spikelets

© JMD

Tall fescue spikelets in anthesis

© JHM&TB

Tall fescue plant(s)

© JHM&TB

Tall fescue leaf collar region

© JHM&TB
38

Uruguayan Pampas Grass 

Cortaderia selloana (Schult. & Schult. f.) Asch. & Graebn. 

(Grass family, Poaceae)

Description

Very large, cespitose, perennial, warm-season bunchgrass, very 

large to about 6-1/2 to 23 feet tall; leaves are narrow 1/2 to 3/4 inch 

wide but up to 6-1/2 to 10 feet long; grows in large clumps about 

12 feet in diameter, with many individual plants within; deep green 

leaves are razor sharp, capable of cutting just by rubbing against them.

Plants: Culms 6-1/2 to 23 feet tall, erect, densely clumped; leaves 

primarily basal; sheaths open, often overlapping, glabrous or hairy; 

auricles absent; ligules of hairs; bluish-green blades from 6-1/2 to 10 

feet long, flat to folded, 1 to 3 inches wide, arching, edges usually 

sharply serrate. 

Inflorescence/Spikelet/Floret: Flowers July to August; 

inflorescences terminal, white to pinkish, plume-like panicle, 12 to 

51 inches long, subtended by a long, ciliate bract; branches stiff to 

flexible; spikelets somewhat laterally compressed, usually unisexual, 

sometimes bisexual, with 2 to 9 unisexual florets; disarticulation 

above the glumes and below the florets; glumes unequal, nearly as 

long as the spikelets, hyaline, 1-nerved; calluses pilose; lemmas 

3- to 7-nerved, long-acuminate, bifid and awned, or entire and sharppointed; lemmas of female and bisexual florets usually long-silken; 

lemmas of staminate florets less hairy or glabrous; lodicules 2, wedgeshaped and irregularly lobed, ciliate; paleas about half as long as the 

lemmas, 2-nerved.

Habitat

Established in moist places such as ditches, stream and riverbanks, 

and flood plains, growing best in well drained soils where abundant 

moisture is available; within elevations that generally range below 

7,000 feet.

Propagation/Phenology

Reproduces by seed and vegetatively; lateral roots can spread to 

13 feet in diameter and 11-1/2 feet in depth; one plant can produce 

over 1 million seeds during its lifetime.
39

Grasses

Comments

Native to South America; once established, roots of a 

single plant can occupy a soil area of about 1,100 square feet; 

Uruguayan pampas grass grows rapidly, is highly competitive, 

and can be difficult to control. New Mexico Watch List species.

Uruguayan pampas grass 

inflorescences (male right, 

female left)

© JMD

Uruguayan pampas grass leaf 

collar region

© JMD

Uruguayan pampas grass 

female plants

© JMD

Uruguayan pampas grass female 

inflorescences

© JV
40

Weeping Lovegrass

Eragrostis curvula (Schrad.) Nees (Grass family, Poaceae)

Description

Weeping lovegrass is a large, rapidly growing warm-season 

perennial bunchgrass, 18 to 75 inches tall; the many long, narrow leaves 

emerging from a tight tuft are pendulous, with the tips almost touching 

the ground; the drooping leaf characteristic gives rise to the name 

“weeping” lovegrass.

Plants: Erect culms are glabrous or glandular; leaf sheaths with 

scattered hairs to 3/8 inch long inside the upper margin and along the 

collar; ligules less than 1/16 inch long; leaf blades 4-3/4 to 25-1/2 inches 

long, not more than 1/8 inch wide, flat to rolled inward, stiff and finely 

pointed; lower surfaces glabrous, upper surfaces with scattered hairs, 

hairs to 1/4 inch long. 

Inflorescence/Spikelet/Floret: Flowers July to October; 

inflorescence an open panicle, 6-5/16 to 15-3/4 inches long and 1-9/16 

to 3-1/8 inches wide; primary branches 1-3/16 to 5-1/2 inches long, 

diverging; spikelets 1/8 to 3/8 inch long, less than 1/16 inch wide, linearlanceolate, leaden, yellowish to gray-green in color, with 3 to 15 florets; 

glumes lanceolate, hyaline; both lower and upper glumes less than 

or equal to 1/8 inch long; lemmas also less than 1/8 inch long, ovate, 

membranous, with an acute tip, awnless, lateral nerves are conspicuous.

Habitat

Cultivated and disturbed or degraded sites in meadows, grasslands, 

and at the margins of chaparral, woodland, forest communities, and 

roadsides within elevations that generally range from 6,000 to 8,000 

feet.

Propagation/Phenology

Reproduces by seed; prolific and early seed production is common 

in weeping lovegrass stands.

Comments

Native to southern Africa; weeping lovegrass can establish from 

seed on burned sites. Although weeping lovegrass seed dispersal is 

limited, if stands occur near burned sites, there is high potential for 

establishment. This species generally occurs as a weed in wildland areas 

of the Southwestern Region rather than as an invasive plant.
41

Grasses

Weeping lovegrass inflorescences

© JHM

Weeping lovegrass inflorescences

© JHM

Weeping lovegrass leaf 

collar region

© JMD

Weeping lovegrass bunchgrass

© F&KS
42

Wild Oat

Avena fatua L. (Grass family, Poaceae)

Description

Wild oat is an erect, cool-season annual bunchgrass with open 

branched, nodding flower clusters. It does not have creeping stolons 

or rhizomes; however, it has an extensive fibrous root system.

Plants: Culms 3-1/8 to 63 inches tall, prostrate to erect when 

young, becoming erect at maturity; basal leaf sheaths with scattered 

hairs, upper leaf sheaths glabrous; ligules less than 1/8 to 1/4 inch 

long, acute; blades 4 to 18 inches long, 1/8 to 9/16 inch wide, 

scaberulous.

Inflorescence/Spikelet/Floret: Flowers March to June; 

inflorescence is a panicle, 2-3/4 to 16 inches long, 2 to 8 inches wide, 

open, nodding; spikelets 3/4 to 1-1/4 inches long with 2, sometimes 

3 florets, disarticulation occurs beneath each floret; glumes unequal, 

3/4 to 1-1/4 inches long, 9 to 11 nerved; calluses bearded with hairs 

to 1/4 the length of the lemmas; lemmas 9/16 to 7/8 inch long, 

usually dense with stiff hairs below mid-length, varying to sparsely 

stiff haired or glabrous, nerves not extending beyond the apices; 

apices usually bifid, teeth less than 3/32 inch long; awns 7/8 to 1-5/8 

inches, arising in the middle third of the lemmas.

Habitat

Cultivated and disturbed or degraded sites in desert and 

semidesert grasslands and woodland communities, and roadsides 

within elevations that generally range from 2,500 to 7,200 feet.

Propagation/Phenology

Reproduces by seed. Wild oats can produce roughly 19,400 seeds 

per pound.

Comments

Native to Europe and central Asia; wild oats has excellent forage 

quality. Wild oats is known to cause hay fever and asthma, and 

can cause nitrate accumulation and photosensitivity. This species 

generally occurs as a weed in wildland areas of the Southwestern 

Region rather than as an invasive plant.
43

Grasses

Wild oat spikelets

© SD

Wild oat leaf collar region

© RO

Wild oat floret

© SD

Wild oat plant(s)

© SD
44
Shrubs and Trees

45

Siberian elm © RO
46

African Sheepbush

Pentzia incana (Thunb.) Kuntze (Aster family, Asteraceae)

Description

African sheepbush is a 1 to 1-1/2 foot tall, multiple branched, 

perennial shrub with grayish leaves covered with matted hairs. Stems 

arch downward and can root where the nodes touch the soil.

Leaves: Leaves opposite or fascicled, once pinnatifid, tri-fid at 

the apex, 3/8 to 3/4 inch long, marked with pits, revolute margins, 

and covered with grayish matted hairs; aromatic with a pineapple 

scent.

Flowers: Flowers April to September; flowering peduncles 

slender, 3/4 to 1-3/16 inches long, proximally bracteate, bracts 

remote, appressed, leaflike; small yellow discoid flowers are 

in terminal heads 3/16 inch in diameter, enclosed by graduated 

phyllaries.

Fruit: Fruits are 5-angled achenes with cup-shaped, scarious 

crowns of scales; seeds are greyish white, less than 1/16 inch long; 

there are many on a single flower head.

Habitat

African sheepbush occurs in dry disturbed sites such as waste 

places, pastures, and along roadsides within deserts, semidesert 

grasslands, chaparral, piñon-juniper woodlands, and oak scrub within 

elevations that generally range below 5,300 feet.

Propagation/Phenology

Reproduces by seed and by rooting at nodes on branches that 

come in contact with the soil.

Comments

Native to southern Africa; African sheepbush was introduced in 

Arizona from southern Africa by the USDA NRCS. It is valued in its 

native region as a browse plant. This species generally occurs as a 

weed in wildland areas of the Southwestern Region rather than as an 

invasive plant.
Shrubs and Trees

47

African sheepbush flower heads

© PF

African sheepbush 

foliage

© PF

African sheepbush 

plant

© PF

 African sheepbush 

flower head

© RS
48

African Sumac 

Rhus lancea L. f. (Sumac family, Anacardiaceae)

Description

Slow growing single or multi-stemmed, evergreen tree, 15 to 

30 feet tall; has a graceful, weeping form and dark, fissured bark; 

older specimens, the dark gray bark has fissures that show beautiful 

reddish and orange mahogany color hues. Branches are reddish to 

brownish-gray.

Leaves: Alternate, palmately compound in groups of 3 leaflets 

(tri-foliate) 2 to 5 inches long; petioles 1 to 1-3/16 inches long; 

leaflets subsessile, narrowly lanceolate, entire to slightly serrate, 

1-9/16 to 4-15/16 inches long and 3/16 to 3/8 inch wide, entire, 

leathery, dark shiny green above, pale-green beneath, glabrous; tips 

pointed; bases narrowly, margins smooth.

Flowers: Flowers June to September; dioecious; female plants 

bear small (less than 1/8 inch long), greenish-white flowers in 

panicles; open panicles 3/4 to 3-1/2 inches long (shorter than the 

leaves).

Fruit: Small (up to 3/16 inch diameter), round, slightly flattened 

yellow or red wrinkled drupes grow in clusters; fruit contains small 

black seeds.

Habitat

Cultivated and disturbed or degraded well drained sites in 

woodlands, grassland margins, and riparian communities within 

elevations that generally range below 2,000 feet.

Propagation/Phenology

Reproduces by seed.

Comments

Native to southern Africa; very drought tolerant once established. 

This species generally occurs as a weed in wildland areas of the 

Southwestern Region rather than as an invasive plant. 
Shrubs and Trees

49

African sumac flowers

© X

African sumac foliage and 

flowers

© B&LC

African sumac bark and foliage

© X

African sumac 

tree

© G&AD
50

Camelthorn

Alhagi maurorum Medik. (Pea family, Fabaceae)

Description

Spiny, highly branched, green perennial shrub, 1-1/2 to 4 feet 

tall, with simple, alternate, wedge-shaped leaves; stems are striate 

with slender spines 1/4 to 1-3/4 inches long; with an extensive root 

system; plants spread rapidly by clonal vegetative reproduction from 

vigorous rhizomes.

Leaves: Leaves alternate, sparse, simple, thick, leathery, elliptic 

or obovate in shape, and 5/16 to 1-3/16 inches long, and 1/8 to 1/2 

inch wide; petioles less than 1/8 inch long and stipules about 1/16 

inch long; upper leaf surfaces glabrous, sometimes sparsely hairy, 

and covered with minute red dots; lower leaf surfaces are sparsely to 

moderately covered with hairs.

Flowers: Flowers June to July; 2 to 6 short-stalked flowers 

are produced alternately along each thorn branchlet axis; flowers 

small, pea-like, with magenta to pink petals about 5/16 inch long; 

occurring on spine-tipped branches along the upper portion of the 

plant; sepals persistent, fused and cup-like, with small unequal teeth; 

self-fertilizing.

Fruit: Fruit is a slender, curved, reddish-brown, jointed seedpod, 

3/8 to 1-3/16 inches long; constricted between seeds and often tipped 

with a small spine; seeds 5 to 8, oval, yellowish or greenish-brown 

with dark mottling or solid dark brown, smooth-textured, about 1/8 

inch long, and nearly as wide; both soft- and hard-coated seeds are 

produced.

Habitat

Cultivated and disturbed or degraded dry or moist sites in 

meadows, grasslands, and riparian communities within elevations 

that generally range from 4,500 to 5,000 feet.

Propagation/Phenology

Reproduces mostly by vegetative clones from vigorous rhizomes, 

occasionally from seed; woody root system can grow more than 6 

feet deep and to a distance of 24 feet or more in all directions.
Shrubs and Trees

51

Comments

Native to the Mediterranean region and western Asia; 

once established camelthorn colonies are difficult to control or 

eliminate. Arizona prohibited/restricted noxious weed, New 

Mexico Class A noxious weed, and Texas noxious plant.

Camelthorn flowers and leaves

© JMR

Camelthorn stem, 

leaves, and fruit

© JMR

Camelthorn stems and thorns

© SD

Camelthorn plant

© JMR
52

Himalayan Blackberry

Rubus armeniacus Focke (Rose family, Rosaceae)

Description

An erect, spreading, or trailing, perennial evergreen shrub reaching 

heights of 10 feet or more; purplish-red stems are covered with heavy, 

broad-based prickles 3/16 to 3/8 inch long and the larger stems are 

distinctly 5-angled; stems grow to a height of about 18 inches or more 

before they arch over and trail on the ground for up to 30 feet or more; 

new plants develop where first year stem-nodes touch the ground; this 

plant forms dense thickets that become impenetrable.

Leaves: Leaves are alternate, palmately compound (3 to 5 leaflets), 

persistent, 2-3/4 to 7-7/8 inches long; leaflets are oval, 1-1/2 to 3 inches 

long, dark green above with a heavy white bloom below, margins 

coarsely serrate; rachis and petiole armed with heavy, recurved prickles.

Flowers: Flowers June to August; white or pale pink flowers on 

flat-topped panicles of 3 to 20 together on the tips of the second-year 

side shoots, five broad petalled flowers 3/4 to 1 inch in diameter. 

Fruit: The roundish fruit are aggregate, shiny, large, black drupelets 

from 1/2 inch up to 3/4 inch long, with large succulent drupelets; each 

drupe includes one seed; the fruit is edible.

Habitat

Cultivated and disturbed or degraded sites in meadows, grasslands, 

woodlands, and forest communities, and roadsides in practically 

any kind of soil containing loam, sand, or gravelly material within 

elevations that generally range from 4,000 to 8,500 feet.

Propagation/Phenology

Reproduces vegetatively or by seed; new stems are capable of 

rooting; thickets can produce 7,000 to 13,000 seeds per square yard, and 

good seed crops occur nearly every year.

Comments

Native to Eurasia; among the many native blackberries and 

raspberries, one can differentiate Himalayan blackberry by the five 

leaflets and curved spines with wide bases. This blackberry species 

also has furrowed, angled stems while others are typically round. 

This species generally occurs as a weed in wildland areas of the 

Southwestern Region rather than as an invasive plant.
Shrubs and Trees

53

Himalayan 

blackberry fruit 

and foliage (left)

© RO

Himalayan 

blackberry 

flowers and 

foliage

© JMR

Himalayan blackberry leaves 

(underside) and prickles 

(above)

© F&KS

Himalayan blackberry flower

© RO
54

Lilac Chastetree

Vitex agnus-castus L. (Verbena family, Verbenaceae)

Description

A large, deciduous, multistemmed, irregular to rounded shrub or 

small tree, from 15 to 20 feet tall, and from 10 to 15 feet in diameter. 

Twigs are slender, opposite, gray-brown and pubescent, four sided; 

buds are wedge shaped to rounded and gray-brown. Bark isinitially 

smooth and gray-brown, becoming blocky on older stems.

Leaves: The aromatic leaves are opposite, palmately compound 

(5 to 7 leaflets), 2 to 6 inches in diameter, leaflets are linear, lance 

shaped, toothed; typically grey-green to dark green above and lighter 

on the undersides. 

Flowers: Flowers May to September; branched flower clusters 4 

to 12 inches long, 1/2 to 1-1/4 inches wide; color ranges from violet 

to blue to deep purple, 1/4 to 3/8 inch long; slightly curved, funnelshaped flowers are fragrant.

Fruit: Round, green and fleshy, drying and turning brown, 1/8 

inch in diameter, persistent through winter; containing four seeds.

Habitat

Woodlands and dry areas in almost any soil that has good 

drainage within elevations that generally range below 8,500 feet.

Propagation/Phenology

Reproduces by seed; average 40,000 seeds per pound.

Comments

Native to southern Europe and western Asia. Not only is the 

tree strikingly beautiful when in full bloom, but it is also fragrant 

and attracts pollinating bees, and hummingbirds make hungry visits. 

The leaves also bear a striking resemblance to those of the infamous 

marijuana or hemp (Cannabis spp. L.) plant. Lilac chastetree has 

been used for thousands of years for its beneficial effect on the 

female hormonal system. This species generally occurs as a weed in 

wildland areas of the Southwestern Region rather than as an invasive 

plant.
Shrubs and Trees

55

Lilac chastetree foliage

© LR

Lilac chastetree mature fruit

© HZ

Lilac chastetree 

flowering stalk and 

foliage

© HZ

Lilac chastetree flowers 

and foliage

© HZ
56

Russian Olive

Elaeagnus angustifolia L. (Oleaster family, Elaeagnaceae)

Description

Deciduous, usually thorny shrub or small tree to 35 feet tall; 

stems, buds, and leaves have a dense covering of silvery to rusty 

scales; at 3 years of age, plants begin to flower and fruit.

Leaves: Leaves are petiolled, alternate, simple, lanceolate to 

elliptical, 7/8 to 4 inches long and 1/2 to 3/4 inch wide, bright green 

above, silvery and scaly beneath, margins entire.

Flowers: Flowers June to July; male and female flowers borne 

on separate plants; very fragrant, silvery, pale yellow, 9/16 to 1-1/16 

inch flowers usually arise in the axils of the leaves.

Fruit: Fruit is a yellow-silvery, scaly, oval shaped drupe, 5/16 to 

1/2 inch long.

Habitat

Found along streams, fields, ditches, roadsides, and open areas 

in a variety of soil types and moisture conditions, including bare 

mineral substrates within elevations that generally range from 4,000 

to 7,500 feet.

Propagation/Phenology

Establishment and reproduction of Russian olive is primarily 

by seed, although some vegetative propagation may also occur; 

the small cherry-like fruit of Russian olive is readily eaten and 

disseminated by many species of birds.

Comments

Native to Eurasia; Russian olive can out-compete native 

vegetation, interfere with natural plant succession and nutrient 

cycling, and tax water reserves; because Russian olive is capable of 

fixing nitrogen in its roots, it can grow on bare, mineral substrates 

and dominate riparian vegetation where overstory cottonwoods have 

died. New Mexico Class C noxious weed.
Shrubs and Trees

57

Russian olive flowers and 

foliage

© PWI

Russian olive fruit and foliage 

(lower left)

© PB

Russian olive tree (lower right)

© CE

Russian olive bark (left)

© PB
58

Saltcedar

Tamarix spp. L. (Tamarix family, Tamaricaceae)

Description

Deciduous or evergreen shrubs or small trees reaching 5 to 20 

feet tall and forming dense thickets; saltcedar are characterized by 

slender, long branches and gray-green foliage; bark of young trees 

is smooth and reddish-brown, as the plant ages, the bark becomes 

brownish-purple, ridged and furrowed. 

Leaves: Leaves are small (about 1/16 inch long), scale-like, 

alternate and overlap one another, on highly branched, slender stems.

Flowers: Flowers March to September; large numbers of pink to 

white flowers, about 1/16 inch across, appear in a dense mass on 1/2 

to 2 inch long spikes at branch tips.

Fruit: Greenish-yellow to pinkish-red capsules, 1/8 to 3/16 inch 

long, which split into 3 to 5 parts on maturity; seeds are less than 

1/16 inch long, with a tuft of fine hairs at one end; the number of 

seeds per capsule is not constant; seeds are dispersed by wind to new 

locations.

Habitat

Tamarisk occurs in moist meadow and riparian communities, 

in drainage washes of natural or artificial water bodies, and in 

other areas where seedlings can be exposed to extended periods of 

saturated soil conditions for establishment; can grow on soils with 

up to 15,000 ppm soluble salt within elevations that generally range 

below 7,500 feet.

Propagation/Phenology

Reproduces primarily by seed, but root crowns can produce new 

shoots, especially when severed; seeds are dispersed by wind to new 

locations; seedlings require extended periods of soil saturation for 

establishment.

Comments

Native to Eurasia and Africa; heavy infestations of saltcedar 

are difficult to control; established plants have long roots that can 

tap deep water tables; absorbs large amounts of water and creates 

large deposits of salt. New Mexico Class C noxious weed and Texas 

noxious and invasive plant.
Shrubs and Trees

59

Saltcedar flowers (left)

© JMR

Saltcedar twig and 

foliage (left)

© BM

Saltcedar 

bush in flower 

(right)

© SD

Saltcedar tree 

(right)

© JMR
60

Siberian Elm

Ulmus pumila L. (Elm family, Ulmaceae)

Description

Siberian elm is usually a small to medium sized, often bushy, 

tree growing 30 to 70 feet tall, with an open crown; trunks up to 32 

inches in diameter; leaves are deciduous in cold areas, but semievergreen in warmer climates; bark is gray or brown, with shallow 

furrows at maturity; both the buds and twigs are nearly hairless; tree 

is short lived in temperate climates, rarely reaching more than 60 

years of age.

Leaves: Leaves are simple, alternate generally less than 2-3/4 

inches long and 1-3/16 inches wide, with an asymmetrical-oblique 

base and a coarsely serrated margin, with a pointed tip; glabrous leaf 

petioles are less than 3/16 inch long, changing from dark green to 

yellow in autumn.

Flowers: Flowers March to April; flowers are greenish, 

lack petals, and occur in small tightly drooping clusters of 2 to 5 

blossoms; flowers appearing before the leaves.

Fruit: The wind-dispersed fruit develops in a flat, oval 

membranous wing, pale green samara, 3/8 to 9/16 inch in diameter, 

notched at the outer end; fruit has one seed that is circular or ovate 

with a smooth surface; fruit hang in clusters; becoming yellow-cream 

to tan colored with age.

Habitat

Cultivated and disturbed or degraded sites in meadows, 

grassland, woodland, and riparian communities, and roadsides on 

well-drained soils within elevations that generally range below 8,100 

feet.

Propagation/Phenology

Reproduces by seed and root suckering; fruits develop quickly 

and are disseminated by wind, allowing the species to form thickets 

of hundreds of seedlings in bare ground; seeds germinate readily and 

seedlings grow rapidly. 

Comments

Native to eastern Asia; once established, Siberian elm is 

extremely difficult to eradicate. New Mexico Class C noxious weed.
Shrubs and Trees

61

Siberian elm 

fruit

© USDA2

Siberian elm leaves (above)

© JMR

Siberian elm 

twigs, buds, 

and foliage

© RO

Siberian elm tree(s)

© RO
62

Sweet Resinbush

Euryops multifidus (Thunb.) DC. (Aster family, Asteraceae)

Description

Sweet resinbush is a low growing, medium sized, cool-season 

shrub, usually less than 3 feet tall; the name sweet resinbush comes 

from the sweet, but disagreeable odor of the flowers and the drops of 

resin exuded by the woody stems.

Leaves: Foliage is bright green, glabrous, except for woolly tufts 

of hair in the leaf axils; linear leaves are linear, about 9/16 inch long; 

with 3 to 6 narrow lobes at the tip, which may look like tiny turkey 

tracks; has foliage in winter and spring, then sheds its leaves during 

the dry season.

Flowers: Flowers January to February; yellow flower heads are 

about 3/8 inch wide on stalks 1 to 6 inches long; leaves and flower 

heads are mostly clustered at the ends of short branchlets; flower 

head bracts are slightly fused at the base; when in bloom, hundreds 

of small, daisy-like flower heads may hide any green leaves.

Fruit: Hawk’s eye has fruit with deciduous, soft pappus bristles 

that have conspicuously long barbs; flowers produce an abundance of 

seed. The seeds form in star-like clusters of about 10 fruits covered 

with fine hairs.

Habitat

Semiarid grassland, desert grassland, desert shrub, and desert 

scrub habitats below the Mogollon Rim in Arizona.

Propagation/Phenology

Reproduces by seed.

Comments

Native to South Africa; creates monocultures, excluding native 

species. Arizona restricted noxious weed.
Shrubs and Trees

63

Sweet resinbush flowers

© EM

Sweet resinbush flowers

© EM

Sweet 

resinbush 

foliage and 

mature 

flowers

© HB

Sweet 

resinbush 

plant

© HB
64

Tree of Heaven 

Ailanthus altissima (Mill.) Swingle 

(Quassia family, Simaroubaceae)

Description

Usually a small to medium sized, fast growing, deciduous tree 

40 to 90 feet tall, open canopy spread 35 to 50 feet; trunks up to 36 

inches in diameter; few, coarse branches, smooth stems with pale 

gray thin bark; twigs which are light chestnut brown, especially in 

the dormant season; all parts of the tree, especially the leaves and 

flowers, have a nutty or burned nut odor. 

Leaves: Leaves evenly pinnately compound, large to 1 to 4 feet 

in length; alternate and composed of 10 to 41 smaller leaflets, 4 to 

8 inches long and 2 to 4 inches wide; each leaflet has one or more 

glandular teeth along the lower margin; margins are otherwise entire 

or lacking teeth, ciliate. 

Flowers: Flowers April to June; tree of heaven is dioecious, 

male and female flowers occur on separate plants; flowers occur in 

large terminal clusters 8 to 16 inches in diameter; flowers are small 

green to pale yellow, turning bright red to brown when ripe.

Fruit: Fruits grow in clusters of 1-seeded, dry samaras, 

resembling maple fruits, 1-1/2 inches long, on female trees; flat, 

twisted, winged fruits each containing a single central seed.

Habitat

Cultivated and disturbed or degraded moist sites in washes, 

meadows, grasslands, woodlands, and forest communities, and 

roadsides within elevations that generally range below 6,200 feet.

Propagation/Phenology

Tree of heaven is a fast growing, prolific seed producer; an 

individual tree can produce as many as 325,000 seeds per year; as 

well as a persistent stump and root sprouter.

Comments

Native to China; once established, tree of heaven is difficult to 

control; it also produces chemicals that prevent the establishment of 

other plant species nearby; plant looks similar to native walnut. New 

Mexico Class B noxious weed.
Shrubs and Trees

65

Tree of heaven foliage 

and flowers

© JM

Tree of 

heaven foliage 

and fruit

© CB

Tree of heaven plant

© RO

Tree of heaven bark

© PWI
66
67

Green or Inconspicuous Flowered Forbs

Russian thistle © MEH
68

Common Cocklebur

Xanthium strumarium L. (Aster family, Asteraceae)

Description

Warm-season annual forb 2 to 4 feet tall and little branched, 

except for short side stems appearing from the leaf axils; stems round 

or slightly ribbed; often speckled with purple and have short white 

hairs scattered across the surface; root system consists of a taproot 

that is stout and rather woody.

Leaves: The alternate leaves are up to 8 inches long and 6 inches 

across; cordate or ovate-cordate shaped, with bases that are well 

rounded or indented and tips that are broad and blunt; margins are 

shallowly lobed or coarsely toothed, while the upper surface has a 

sandpapery texture; each leaf has a long petiole that is often reddish 

or reddish green and about as long as the leaf blade; petioles usually 

have short white hairs.

Flowers: Flowers July to September; flower heads are small; 

in the axils of the upper leave; flowers are of two types, male and 

female flower heads separate; male flower heads about 1/4 inch 

across, female flower heads about 1-1/2 inches long and 1 inch 

across; flowers are green.

Fruit: Fruits are a 3/8 to 13/16 inch long, woody bur, with 

hooked prickles and 2 curved spines at the tip; 2-seeded; dark brown 

seeds are flattened and pointed at the tips.

Habitat

Cultivated and disturbed or degraded dry sites in meadows, 

grasslands, woodlands, and chaparral communities, and roadsides 

within elevations that generally range below 6,300 feet.

Propagation/Phenology

Reproduces by seed; cocklebur is one of nature’s original 

“velcros.”

Comments

Native to North America; young seedlings of common cocklebur 

exude toxic chemicals that can inhibit germination of other species 

of plants, or kill off their seedlings; individual plants become less 

toxic as they mature: spiny cocklebur is a closely related and similar 

species, however, unlike common cocklebur, this weed has the very 
69

Green or Inconspicuous Flowered Forbs

Common cocklebur 

immature fruit and foliage 

(below)

© RV Common cocklebur plants

© RV

distinctive 3-parted spines that arise at the base of each leaf. 

This species generally occurs as a weed in wildland areas of 

the Southwestern Region rather than as an invasive plant. 

Common cocklebur flower 

head

© PW2

Common cocklebur 

mature fruit

© JS
70

Eurasian Watermilfoil 

Myriophyllum spicatum L. 

(Water Milfoil family, Haloragaceae)

Description

Eurasian watermilfoil is an emergent, herbaceous aquatic plant; 

stems grow to the water surface, usually extending 3 to 10 feet, but 

as much as 33 feet in length; stems are long, slender, branching, 

reddish-brown to whitish-pink, hairless, and become leafless 

toward the base; roots fibrous; often developing on plant fragments; 

frequently forming dense mats.

Leaves: Grayish-green leaves are 4-whorled, highly dissected, 

composed of 28 to 48 threadlike divisions about 1/2 to 2 inches long; 

leaflets give milfoil a feathery appearance that is a distinguishing 

feature of the plant.

Flowers: Flowers July to August; flowering spikes emerge above 

the water 2 to 4 inches; flowers are borne in the axis of bracts; are 

either 4-petalled or without petals.

Fruit: The fruit is a hard, segmented capsule containing 4 seeds.

Habitat

Lakes, ponds, shallow reservoirs, and low energy areas of rivers 

and streams within elevations that generally range below 4,000 feet.

Propagation/Phenology

Reproduction is by seed, fragmentation, and winter buds; 

however, the primary form of regeneration is from rhizomes, 

fragmented stems, and axillary buds that develop throughout the 

year.

Comments

Native to Eurasia; Eurasian watermilfoil can form large, floating 

mats of vegetation on the surface of lakes, rivers, and other water 

bodies, preventing light penetration for native aquatic plants and 

impeding water traffic. M spicatum can easily be mistaken for the 

submersed form of M. aguatic. New Mexico Class A noxious weed 

and Texas noxious plant.
71

Green or Inconspicuous Flowered Forbs

Eurasian watermilfoil 

inflorescence

© LJM

Eurasian watermilfoil foliage

© RO

Eurasian watermilfoil 

plants

© AF

Eurasian 

watermilfoil 

infestation

© LJM
72

Halogeton

Halogeton glomeratus (M. Bieb.) C. A. Mey 

(Goosefoot family, Chenopodiaceae)

Description

Erect, highly branched, toxic winter to summer annual with small, 

fleshy leaves, ranging from a few inches to 19 inches tall; branches 

often curved at the base, ascending to erect, plants are blue-green, 

stems usually tinged reddish or purple.

Leaves: Small, fleshy leaves alternate, sessile, dull green to 

bluish-green, cylindrical, 3/16 to 7/8 inch long, usually less than 1/16 

inch wide, broadest at the apex; apex bluntly rounded, tipped with 

a stiff bristle usually less than 1/16 inch long; blue-green foliage 

glabrous, except for tufts of long white interwoven hairs in the leaf 

axils.

Flowers: Flowers June to September; flowers are green and 

inconspicuous; however, flower clusters are numerous and dense in 

most leaf axils, with 0 to 3 bractlets less than 1/16 inch long below 

each cluster.

Fruit: Utricles (thin-walled 1-seeded fruits), usually less than 

1/16 inch long, enclosed by sepals; fruits with sepals typically hide 

stems; utricles contain blackish-brown seeds; seeds are teardropshaped, often with 2 points, flattened, usually less than 1/16 inch long.

Habitat

Cultivated and disturbed or degraded alkaline and saline soils in 

open sites within grassland and woodland communities, and roadsides 

within elevations that generally range from 4,000 to 6,500 feet.

Propagation/Phenology

Reproduces by seed; plants typically produce enormous quantities 

of seed, average is roughly 75 seeds per inch of stem; most seeds 

germinate late fall to early spring in cold winter areas, but some 

germination can occur year round when conditions become favorable.

Comments

Native to the cold desert regions of Eurasia; halogeton competes 

poorly with established perennial vegetation. Arizona prohibited/

restricted noxious weed and New Mexico Class B noxious weed.
73

Green or Inconspicuous Flowered Forbs

Halogeton flowers

© CS

Halogeton foliage (left)

© BM

Halogeton foliage (below)

© BM

Halogeton 

plant (right)

© BM
74

Kochia

Bassia spp. L. (Goosefoot family, Chenopodiaceae)

Description

Annual warm-season forb with spreading taproot; stems bushy, 

much branched, 1 to 6 feet tall, 1 to 5 feet in diameter, unusually 

soft, hairy, round, often reddish-tinged.

Leaves: The simple, alternately arranged leaves are linear to 

narrowly ovate 1/2 to 2 inches long and 5/16 inch wide, very short 

petioled or sessile, margins fringed with hairs, upper surface usually 

smooth, lower usually covered with soft hairs, leaf blades with 3 to 5 

conspicuous veins; stems may be green, red tinged, or red depending 

on age.

Flowers: Flowers July to October; flowers small, greenish, 

sessile in the axils of the upper leaves and form short, dense, bracted 

spikes, 3/16 to 3/8 inch long.

Fruit: Kochia is an abundant seed producer; seeds are dull 

brown, less than 1/16 inch wide and contained in a star-shaped fruit.

Habitat

Cultivated and disturbed or degraded sites in grassland and 

woodland communities, and roadsides in any type of well drained, 

uncompacted soil, within elevations that generally range below 8,500 

feet.

Propagation/Phenology

Reproduces by seed. Kochia is a highly effective reproducer. 

After seeds mature in late fall, the plant stem separates from the root, 

the plant is then blown by wind and seeds—held in the leaf axils—

fall to the ground as the plant tumbles.

Comments

Native to Europe and western Asia; kochia aids in spreading fire; 

burns easily because stems are spaced in an arrangement that allows 

for maximum air circulation; dead plants contribute to fuel load by 

retaining their original shape for some time before decomposing. 

Because it is extremely efficient at using water, it thrives in warm, 

low rainfall environments. Although palatable to stock, kochia may 
75

Green or Inconspicuous Flowered Forbs

Kochia plant(s)

© LR

Kochia plant(s)

© JMR

be toxic in large quantities. In general appearance this species 

could be confused with Russian thistle. This species generally 

occurs as a weed in wildland areas of the Southwestern Region 

rather than as an invasive plant.

Kochia flowers and 

foliage

© RO

Kochia plants

© RO
76

Parrot Feather Milfoil

Myriophyllum aquaticum (Vell.) Verdc. 

(Water Milfoil family, Haloragaceae)

Description

Parrot feather milfoil is an aquatic perennial, herbaceous, rooted, 

submerged to emergent plant that invades shallow aquatic habitats 

throughout much of the United States. Stems, up to 5 feet long, trail 

along the ground or water surface, becoming erect and leafy at the 

ends. Stems are stout and blue-green in color.

Leaves: Leaves are abundant, 4 to 6 whorled, pinnately 

compound, and finely dissected (feathery looking) with 20 to 30 

divisions per leaf; submersed leaves are 9/16 to 1-3/8 inches long 

and have 20 to 30 divisions per leaf; emergent leaves are 3/4 to 2 

inches long, less divided and greener than the submersed leaves.

Flowers: As only female plants occur in North America, 

reproduction occurs vegetatively; however, inconspicuous flowers 

are formed in the axils of the emergent leaves in the spring 

(sometimes fall).

Fruit: No fertile fruit is known to be produced in the United 

States.

Habitat

Lakes, ponds, shallow reservoirs, and low energy areas of rivers 

and streams within elevations that generally range below 4,000 feet.

Propagation/Phenology

Reproduction occurs vegetatively from whole plants or 

fragments.

Comments

Native to South America, parrot feather milfoil’s potential 

range is yet to be determined. In more southern regions, this plant 

forms monocultures that clog waterways, impeding recreational 

and commercial boating activities. These monocultures also disrupt 

the growth of native aquatic plants and provide breeding areas 

for mosquitoes. The submersed form of M. aquatic can easily be 

mistaken for M. spicatum. Control of this plant is extremely costly. 

New Mexico Class A noxious weed and Texas noxious plant.
77

Green or Inconspicuous Flowered Forbs

Parrot feather 

milfoil emergent 

foliage

© V

Parrot feather 

milfoil plants

© NL

Parrot feather 

milfoil plants

© V

Parrot feather 

milfoil infestation

© F&KS
78

Russian Thistle

Salsola spp. L. (Goosefoot family, Chenopodiaceae)

Description

Annual herb with spreading taproot; stems bushy, much branched, 

1/2 to 4 feet tall, 1 to 5 feet in diameter, rigid, spiny, spherical, often 

reddish-purple in age, young stems and leaves green and succulent.

Leaves: Leaves alternate, the first-formed leaves fleshy, cylindrical 

or awl-shaped, 7/16 to 2-1/2 inches long and less than 1/16 inch wide, 

with a pointed tip, the latter-formed leaves shorter, stiff, dilated and 

thickened at the base, ending in a hard sharp spine.

Flowers: Flowers June to October; flowers small, greenish, mostly 

solitary in the axils; petals none; sepals 5, papery and persistent; 2 

bracts at the base of each flower are rigid, spine-tipped; fruit surrounded 

by the 5 enlarged sepals, each developing a fan-shaped, strongly veined 

wing on its back, 1/8 to 3/8 inch in diameter.

Fruit: Seeds numerous (to 250,000 per plant), top-shaped, 1/16 

inch in diameter, with a yellowish coiled embryo, visible through the 

thin gray wall.

Habitat

Cultivated and disturbed or degraded sites in grassland and 

woodland communities, and roadsides in any type of well-drained, 

uncompacted soil, however, it is most frequent in alkaline or saline 

soils within elevations that generally range below 8,500 feet.

Propagation/Phenology

Reproduces by seed; Russian thistle is a highly effective 

reproducer, after seeds mature in late fall, the plant stem separates from 

the root, the plant is then blown by wind; seeds, held in the leaf axils, 

fall to the ground as the plant tumbles.

Comments

Native to the Mediterranean region; Russian thistle aids in 

spreading fire; burns easily because stems are spaced in an arrangement 

that allows for maximum air circulation; dead plants contribute 

to fuel load by retaining their original shape for some time before 

decomposing. In general appearance, this species could be confused 

with kochia. This species generally occurs as a weed in wildland areas 

of the Southwestern Region rather than as an invasive plant.
79

Green or Inconspicuous Flowered Forbs

Russian thistle flowers

© F&KS

Russian thistle 

flowers and 

foliage (right)

© PTL

Russian thistle plants

© F&KS

Russian thistle 

plants

© MEH
80

Spiny Cocklebur

Xanthium spinosum L. (Aster family, Asteraceae)

Description

Erect, much branched, slender, hairy, warm-season annual reaching 

to 3-1/2 feet in height; taproot; stems have 3-parted spines that arise at 

the base of each leaf; with characteristic “cocklebur” fruit.

Leaves: Alternately, approximately 1 to 2-1/2 inches long and 3/16 

to 1 inch wide; lance-shaped in outline with irregular lobes or teeth along 

the margin; without hairs above, but have many soft white hairs below 

and have conspicuous white veins on the shiny dark green upper leaf 

surfaces; occur on petioles that range from 1/4 to 1 inch in length; very 

distinctive yellow, 3-parted spine 1/2 to 1 inch long occurs at the base of 

each leaf petiole.

Flowers: Flowers December to May; inconspicuous, cream-green 

in color, arising from the area between the leaf petioles and the stems 

(female flowers) and at the ends of the erect stems (male flowers).

Fruit: An elliptic to egg-shaped, 2-chambered bur, 1/2 to 1-1/2 

inches long and covered with hooked prickles. Each bur contains 2 seeds.

Habitat

Cultivated and disturbed or degraded dry sites in meadows, 

grassland, woodland, and chaparral communities, and roadsides within 

elevations that generally range below 6,300 feet.

Propagation/Phenology

Reproduces by seed; of the two seeds in each burr, one germinates 

the first spring or summer and the other does not germinate until 

the second or third year; spiny cocklebur is one of nature’s original 

“velcros.”

Comments

Native to Chile; poisoning has occurred in all classes of domestic 

livestock, and is always associated with cotyledonary seedling ingestion; 

symptoms are anorexia, depression, nausea, and prostration; death 

may occur in a few hours to 3 days after the symptoms are first noted; 

common cocklebur is a closely related and similar species, however, 

unlike spiny cocklebur, this weed does not have the very distinctive 

3-parted spines that arise at the base of each leaf. New Mexico Watch 

List species.
81

Green or Inconspicuous Flowered Forbs

Spiny cocklebur stem, 

spines, and fruits

© JMR

Spiny cocklebur foliage and spines

© JMR

Spiny 

cocklebur 

foliage

© RV

Spiny cocklebur 

plants (right)

© BR
82
Pink, Rose, Red, or Purple Flowered Forbs

83

Hounds-tongue © RV
84

Alfalfa

Medicago sativa L. (Pea family, Fabaceae)

Description

Alfalfa is a long lived, perennial legume; stems decumbent to 

erect from a woody crown to about 8 to 31-1/2 inches tall; new 

growth occurs from buds in the crown; taproot stout.

 Leaves: Leaves are trifoliate compound, alternately arranged on 

the stem; petiole pubescent, 3/16 to 1-3/16 inches long; leaflets 3/8 to 

9/16 inch long, 1/8 to 3/8 inch wide, narrowly lanceolate to obovate, 

glabrous or appressed hairy, paler green beneath; stipules entire to 

sharply toothed, 3/16 to 5/8 inches long, pubescent on lower surface, 

glabrous on upper surface.

Flowers: Flowers March to October; inflorescence spikelike, 5 to 

40 flowered, longer in fruit; calyx 3/16 inch long or less; corolla 5/16 

to 3/8 inch long, purple or multicolored (i.e., violet, violet-green, 

greenish-yellow, rarely yellow).

Fruit: Leathery pods, slightly pubescent or glabrous, 1/8 to 3/8 

inch in diameter, ranging from sickle-shaped to spirals (2 to 3 coils); 

pods contain 6 to 8 small kidney-shaped, yellowish-brown seeds; 

produces roughly 227,000 seeds per pound.

Habitat

Near cultivated fields, meadows, roadsides, disturbed habitats, 

waste places, and on moist soils within elevations that generally 

range from 4,000 to 9,500 feet.

Propagation/Phenology

Reproduces by seed.

Comments

Native to southwest Asia; deep rooting habit (where possible 

as much as 20 feet or more) makes alfalfa a very drought resistant 

plant. Alfalfa has been cultivated for forage worldwide. Alfalfa may 

become weedy or invasive in some regions or habitats and may 

displace desirable vegetation if not properly managed. This species 

generally occurs as a weed in wildland areas of the Southwestern 

Region rather than as an invasive plant. 
Pink, Rose, Red, or Purple Flowered Forbs

85

Alfalfa plant(s)

© HFS

Alfalfa flowers

© KW

Alfalfa trifoliate leaf

© GH

Alfalfa fruit

© RO
86

Black Henbane

Hyoscyamus niger L. (Potato family, Solanaceae)

Description

Erect, coarse, summer annual or biennial, 12 to 39 inches tall; 

foliage is covered with sticky glandular hairs; has a foul odor at all 

growth stages.

Leaves: Stems erect, leafy, branched (biennial form) or few 

branched (annual form), densely covered with long, glandular hairs; 

leaves alternate, gray-green, covered with short glandular hairs, shortstalked (lower) to sessile (upper), oblong to lanceolate, 2 to 8 inches 

long, coarsely toothed to acutely pinnate-lobed, with conspicuous pale 

veins covered with long glandular hairs.

Flowers: Flowers June to September; pale brownish-yellow 

flowers with purple centers and purple veins are found on long 

racemes in the axils of the upper leaves; flowers 5-lobed, fussed, 

funnel-shaped, 3/4 to 1-3/4 inches long.

Fruit: Fruits ovoid to pineapple-shaped, 5-lobed capsule, 1/2 to 1 

inch long; seeds numerous, brown to gray, deeply pitted, and flattened, 

1/16 inch long. 

Habitat

Cultivated and disturbed or degraded open sites in woodland and 

forest communities, and roadsides in sandy or well-drained loam soils 

with moderate fertility within elevations that generally range from 

5,500 to 8,000 feet. 

Propagation/Phenology

Reproduces by seed; seeds that mature early in a season typically 

produce biennial plants; biennial seedlings require a cold moist period 

to induce stem elongation and flowering; seeds maturing late in a 

season often produce annual plants; newly matured seeds germinate 

without light; seeds that become dormant germinate best when 

exposed to light; seed can remain viable for approximately 4 years.

Comments

Native to Eurasia; all plant parts contain tropane alkaloids and 

are toxic to humans and animals when ingested. New Mexico Class A 

noxious weed.
Pink, Rose, Red, or Purple Flowered Forbs

87

Black henbane flowers

© JS

Black henbane flowers 

and seed capsules (right)

© SD

Black henbane foliage 

(above)

© MEH

Black henbane plants 

(left)

© MEH
88

Blue Mustard

Chorispora tenella (Pall.) DC. (Mustard family, Brassicaceae)

Description

Prostrate or erect, single or branched stemmed, clump- or patchforming winter annual forb; 2 to 20 inches tall; shallow to stout 

taproot; seedlings have oval and somewhat glandular leaves.

Leaves: Rosette leaves oblong to oblanceolate, typically sparsely 

covered with minute glandular hairs; foliage sparsely to moderately 

covered with simple, minute glandular hairs that are sticky to touch; 

stems leafy, branched mostly from the base; leaves green, alternate, 

elliptic or oblong to lanceolate or oblanceolate; lower stem leaves 

petioled, 1-1/8 to 1-3/8 inches long, with wavy toothed to pinnately 

lobed margins; upper stem leaves are sessile, with entire to wavytoothed margins.

Flowers: Flowers March to May; flowers showy in elongated 

clusters, 4-petalled, pale purple to bluish-purple, narrowly clawed, 3/8 

to 1/2 inch long; sepals 4, usually purple with narrow membranous 

margins, separate but forming a tube, 1/4 to 5/16 inch long.

Fruit: Fruit is a silique, long upturned, cylindrical capsule with an 

elongated beak about 1-1/8 to 1-3/4 inches long and 1/16 to 3/32 inch 

wide; containing round, reddish-brown spherical seeds 1/16 inch in 

diameter; usually remain within the pod segment.

Habitat

Blue mustard occurs in dry, disturbed sites such as waste places, 

pastures, and along roadsides and railroad rights-of-way within 

elevations that generally range below 7,500 feet.

Propagation/Phenology

Seedlings exist as basal rosettes until flowering stems are 

produced in early spring. Reproduces by seed; viable seeds can be 

produced 10 days after bloom. 

Comments

Native to Eurasia; the plant has a strong scent which is generally 

considered unpleasant. This species generally occurs as a weed in 

wildland areas of the Southwestern Region rather than as an invasive 

plant.
Pink, Rose, Red, or Purple Flowered Forbs

89

Blue mustard infestation

© SD

Blue mustard fruit

© RO

Blue mustard flowers 

(below)

© RO

Blue mustard plant(s) (above)

© AS
90

Bull Thistle

Cirsium vulgare (Savi) Ten. (Aster family, Asteraceae)

Description

Stoutly taprooted, coarse, multibranched annual, biennial or 

short-lived perennial forb, 2 to 6-1/2 feet tall; with stiff, hairy foliage 

and conspicuous prickly-winged stems.

Leaves: Rosette leaves elliptic to oblanceolate, 4 to 16 inches 

long; margins deeply coarse-lobed and toothed; main prickles 3/16 to 

9/16 inch long; stem leaves smaller, more deeply lobed and spinier; 

upper surfaces of all leaves green, evenly covered with stiff, sharppointed hairs, sometimes sparsely cobwebby; lower surfaces covered 

with cobwebby hairs; leaf bases extend nearly all the way down stem 

internodes as conspicuous prickly wings; stems loosely covered with 

white cobwebby hairs, surfaces glandular.

Flowers: Flowers June to October; purple hemispheric to bellshaped flower heads 1 to few, 3/4 to 1-1/2 inches in diameter, loosely 

covered with cobwebby hairs and with at least 1 bract-like leaf just 

below; purple corollas 1 to 1-3/8 inches long; flower head bracts 1 to 

1-1/2 inches long, 3/4 to 1-1/2 inches in diameter lanceolate to linear, 

spreading to reflexed; spines less than 3/16 inch long, yellowish.

Fruit: Achenes 1/8 to 3/16 inch long, ovate to elliptic, slightly 

compressed, smooth, glossy, gray or tan; pappus bristles plumose and 

deciduous, 9/16 to 1-3/16 inches long, white, forming a ring at the 

base and falling as a unit.

Habitat

Cultivated and disturbed or degraded sites in grassland, 

woodland, forest, and riparian communities, and roadsides within 

elevations that generally range from 4,500 to 9,100 feet.

Propagation/Phenology

Reproduces by seed; seeds per flower head range from less than 

100 to more than 400.

Comments

Native to Europe; heavy grazing and disturbances that create 

bare soil patches facilitate seedling establishment and survival. New 

Mexico Class C noxious weed.
Pink, Rose, Red, or Purple Flowered Forbs

91

Bull thistle flower heads

© CE

Bull thistle flower head and 

stems

© CE

Bull thistle plant

© SD

Bull thistle basal rosette

© MS
92

Canada Thistle

Cirsium arvense (L.) Scop. (Aster family, Asteraceae)

Description

Erect clump or patch-forming perennial forb to 39 inches tall, 

with extensive creeping roots and small unisexual flower heads; 

plants are male or female (dioecious), and dense patches of a single 

sex often occur; foliage and stems are spiny.

Leaves: Rosette leaves few or lacking; all leaves oblong to 

lanceolate, 2 to 8 inches long; margins nearly entire to shallowly 

lobed and toothed; main prickles 1/8 to 1/4 inch long; upper surfaces 

glabrous, green; lower surfaces sometimes sparsely woolly; leaf 

bases sometimes extend briefly down stems as inconspicuous prickly 

wings to 3/8 inch long; spiny stems slender, glabrous, and leafy.

Flowers: Flowers June to October; cylindrical or ovoid to bellshaped unisexual flower heads numerous, often clustered; flower 

head bracts 3/8 to 1 inch long, 3/16 to 3/4 inch diameter, often, 

glabrous or with white woolly hair, spines 1/16 inch long; flowers 

pink, purple, or white (males 3/8 to 9/16 inch long, females 9/16 to 

3/4 inch long).

Fruit: Achenes 1/16 to 1/8 inch long, ovate to elliptic, slightly 

compressed, smooth, glossy, tan; pappus bristles plumose and 

deciduous, 9/16 to 3/4 inch long, tan, forming a ring at the base and 

falling as a unit.

Habitat

Cultivated and disturbed or degraded sites in moist grassland, 

woodland, forest and riparian communities, and roadsides within 

elevations that generally range from 4,200 to 8,300 feet.

Propagation/Phenology

Reproduces vegetatively from creeping roots and by seed; root 

reserves are lowest when flowering begins in early summer; new 

roots and shoot buds develop in winter, and shoots emerge in spring; 

subterranean shoots can develop roots and buds at any node; root and 

subterranean shoot fragments 3/8 inch long or more can develop into 

a new plant; female plants only produce viable seed if male plants 

are within pollinator range.
Pink, Rose, Red, or Purple Flowered Forbs

93

Canada thistle female flower 

heads

© SD

Canada thistle plants

© SD

 Comments

Native to Europe; heavy grazing and disturbances that 

create bare soil patches facilitate seedling establishment and 

survival. Arizona prohibited noxious weed, New Mexico Class 

A noxious weed, and Oklahoma noxious weed.

Canada thistle male flower 

heads

© JMR

Canada thistle foliage

© SD
94

Common Burdock

Arctium minus Bernh. (Aster family, Asteraceae)

Description

Common burdock is a warm-season stoutly taprooted biennial 

forb; low growing rosette of basal leaves during the first year, but 

during the second year it becomes 3 to 6 feet tall; second year plant 

is little branched below, but produces short, flowering side stems 

above.

Leaves: Rosette leaves are broadly heart-shaped, 6 to 18 inches 

long, 4 to 14 inches wide, with hollow petioles and wavy and toothed 

margins; undersides are loosely hairy and light green; stem leaves are 

much smaller, alternate, and egg-shaped; upper stems terminate in 

small clusters of flower heads on short stalks.

Flowers: Flowers July to October; flower heads 3/4 to 1 inch 

wide with pink, lavender, purple or white disk flowers, flower head 

bracts with hooked spines curving inward; flowers are enclosed in 

a prickly bur; flowers dry to a bur, and the hooked bracts are often 

confused with a thistle.

Fruit: The 3/16- to 1/4-inch long achenes are oblong, broader 

and more truncate at one end than the other; light brown with dark 

brown speckles; each achene has a crown of fine bristles at the apex.

Habitat

Cultivated and disturbed or degraded sites in meadows, 

grassland, woodland, and riparian communities, and roadsides within 

elevations that generally range below 7,300 feet.

Propagation/Phenology

Insect pollinated; reproduces by seed; one plant can typically 

produce 15,000 seeds. 

Comments

Native to northern Europe; common burdock is one of nature’s 

original “velcros;” burs cling readily to fur and clothing and are 

difficult to remove. This species generally occurs as a weed in 

wildland areas of the Southwestern Region rather than as an invasive 

plant.
Pink, Rose, Red, or Purple Flowered Forbs

95

Common burdock flowers and 

foliage

© MEH

Common burdock plant

© MEH

Common burdock flowers and 

foliage (above)

© RO

Common burdock leaf (left)

© MEH
96

Diffuse Knapweed 

Centaurea diffusa Lam. (Aster family, Asteraceae)

Description

Multi-branched annual or perennial forb, 4 to 31-1/2 inches tall, 

with spiny or comb-like flower head bracts; long taprooted plants 

exist as basal rosettes until erect, highly branched flowering stems are 

produced in late spring/summer.

Leaves: Cotyledons spatulate to oval; rosette leaves pinnatedivided without straw-colored spines at the centers of rosettes; leaves 

alternate, resin-dotted; lower stem leaves deeply 1 to 2 pinnate-lobed, 4 

to 8 inches long; upper stem leaves wingless, entire, linear or bract-like 

3/8 to 3/4 inch long. Foliage variously covered with short to medium 

interwoven gray hairs.

Flowers: Flowers June to September; 1/4 to 3/8 inch diameter 

flower heads solitary or several with 12 to 13 white, pink, or pale 

purple flowers per head, 1/2 inch long; greenish or straw-colored flower 

head bracts overlapping in several rows, 3/8 to 1/2 inch long, tips 

variously spiny or comb-like, central spine spreading, 1/8 inch long.

Fruit: Dark brown achenes oblong, 1/8 to 3/16 inch long, apex 

flattened and tapered to a rounded, laterally notched base, roughly 13 

per head, pappus scales less than 1/16 inch long or lacking.

Habitat

Cultivated and disturbed or degraded well-drained soil sites in 

meadows, grassland, woodland, and forest communities, and roadsides 

within elevations that generally range below 7,200 feet.

Propagation/Phenology

Reproduces by seed, up to 40,000 per plant; germination occurs 

over a broad range of environmental conditions; seeds exhibit three 

germination patterns: nondormant seeds that germinate with or without 

light exposure, dormant seeds that germinate in response to red light, 

and dormant seeds that are not light sensitive.

Comments

Native to southern Europe; diffuse knapweed is a very competitive 

and aggressive plant with allelopathic effects; stands of diffuse 

knapweed may persist indefinitely once established. Arizona prohibited/

restricted noxious weed and New Mexico Class A noxious weed.
Pink, Rose, Red, or Purple Flowered Forbs

97

Diffuse knapweed flower heads

© NER

Diffuse 

knapweed 

foliage 

(above)

© JMD

Diffuse knapweed flower head

© SD

Diffuse knapweed plants (below)

© RO
98

Hounds-tongue

Cynoglossum officinale L. (Borage family, Boraginaceae)

Description

Erect, coarse, 1 to 2 stemmed, biennial or short-lived perennial 

forb, 1 to 4 feet tall, with a thick, black, woody taproot; it forms a 

rosette in the first year and usually flowers in the second year; the 

leaves resemble a hound’s tonge.

Leaves: Basal and lower cauline leaves are petiolate, elliptic to 

oblanceolate, 5-7/8 to 7-7/8 inches long and 3/4 to 2 inches wide, 

tapering at the base; upper leaves are alternate, numerous, gradually 

reduced upward, acute to obtuse, and sessile or clasping, lacking 

teeth or lobes; all leaves are rough and hairy on both surfaces.

Flowers: Flowers May to August; flowers are many on several 

long, 1-sided branches from the upper leaf axils; mature flowers 

stalks are curved, spreading; flowers are dull reddish-purple, broadly 

bell-shaped (5 petals fussed), about 3/8 inch wide and terminal. 

Fruit: Fruit consists of 1 to 4 nutlets, 3/16 to 1/4 inch long, 

rounded-triangular, dorsally flattened, and covered with short, barbed 

prickles; nutlets remain closed at maturity, the seeds remain encased; 

seeds are brown or grayish brown.

Habitat

Cultivated and disturbed or degraded sites in grassland, 

woodland, forest, and riparian communities, and roadsides; it is most 

abundant in areas with more than 10 percent bare ground within 

elevations that generally range from 4,900 to 9,800 feet.

Propagation/Phenology

Reproduces by seed; estimates of total seed produced per plant 

range from 50 to more than 2,000; the barbed nutlet facilitates 

dispersal by animals.

Comments

Native to Europe; hounds-tongue colonizes easily, and quickly 

forms dense monocultures on disturbed habitats; hounds-tongue 

contains pyrrolizidine alkaloids and is toxic to horses and cattle. 

This species generally occurs as a weed in wildland areas of the 

Southwestern Region rather than as an invasive plant.
Pink, Rose, Red, or Purple Flowered Forbs

99

Hounds-tongue flower and fruit

© MEH

Hounds-tongue taproot (left)

© JMR

Hounds-tongue plant in bloom

© RV

Hounds-tongue flowers (above)

© MEH
100

Iberian Knapweed 

Centaurea iberica Trevir. ex Spreng. (Aster family, Asteraceae)

Description

Multi-branched perennial forb, 39 inches tall, with spiny or comblike flower head bracts; stoutly taprooted; plants exist as basal rosettes 

until erect, highly branched flowering stems are produced in late 

spring. 

Leaves: Cotyledons spatulate to oval; rosette leaves pinnatedivided with straw-colored spines at their centers; leaves alternate, 

resin-dotted, lower stem leaves deeply 1 to 2 pinnate-lobed, 4 to 8 

inches long; upper stem leaves wingless, mostly pinnate-divided, 3/8 

to 3/4 inch long. Foliage variously covered with short to medium 

interwoven gray hairs; new leaves green and covered with minute 

bristly hairs.

Flowers: Flowers July to October; 1/4 to 1/2 inch diameter flower 

heads solitary or several with 12 to 13 rose-pink to whitish flowers 

per head, 5/8 to 3/4 inch long; greenish or straw-colored flower head 

bracts overlapping in several rows, 5/8 to 3/4 inch long, tips variously 

spiny or comb-like; central spine stout or spreading, 3/8 to 1 inch long.

Fruit: Whitish achenes oblong, 1/8 to 3/16 inch long, often brown 

streaked, apex flattened and tapered to a rounded, laterally notched 

base; pappus scales less than 1/16 inch long.

Habitat

Often colonizes banks of watercourses and other moist sites within 

elevations that generally range below 3,200 feet.

Propagation/Phenology

Reproduces by seed, up to 40,000 per plant; germination occurs 

over a broad range of environmental conditions; plants produce fewer 

viable seeds in dry years; infestation density correlates with the age 

of the population and degree of disturbance; plants seldom persist in 

shaded places.

Comments

Native to southeast Eurasia; Iberian knapweed is a very 

competitive and aggressive plant with allelopathic effects; stands 

of Iberian knapweed may persist indefinitely once established; old 
Pink, Rose, Red, or Purple Flowered Forbs

101

Iberian knapweed flower heads

© CDFA

Iberian knapweed basal rosettes

© CDFA

Iberian knapweed 

flower head

© CDFA

flower stems can persist after senescence; flower head bracts 

and achenes remaining on old stems can aid with species 

identification when plants are overwintering as rosettes. 

Arizona prohibited noxious weed.

Iberian knapweed pre-bloom 

flower head

© CDFA
102

Meadow Knapweed

Centaurea debeauxii Gren. & Godr. (excluded) 

(Aster family, Asteraceae)

Description

Multi-stemmed, warm-season, perennial forb, 20 to 40 inches 

tall; stems are branched with one flower head at each tip; taprooted.

Leaves: Basal rosette leaves are lance-shaped, up to 6 inches 

long and 1-1/4 inches wide, slightly pubescent, and may be pinnately 

cut or have wavy margins; lower leaves are long-stalked, entire, 

coarsely lobed, or toothed; upper stem leaves are small, stalkless, 

unlobed, and almost bract-like.

Flowers: Flowers May to July; flower heads are solitary, rose 

to purple in color, occasionally white, and almost globe-shaped 5/8 

inch in diameter; underneath the flower head are distinctive roundish, 

light to dark-brown bracts with papery, fringed margins.

Fruits: Fruit is an achene; seeds are about 1/8 inch long, ivorywhite to light brown in color, and sometimes bearing a row of short 

hairs.

Habitat

Cultivated areas and disturbed or degraded sites in meadows, 

grassland and riparian communities, and roadsides; establishes in 

many soil types within elevations that generally range from 3,000 to 

8,000 feet.

Propagation/Phenology

Reproduces primarily through seed production; plant can also resprout from root and crown fragments that have been disturbed.

Comments

Native to Europe; meadow knapweed is considered to be a 

hybrid between brown knapweed (C. jacea L.) and black knapweed 

(C. nigra L.); meadow knapweed is not very palatable to animals; 

once established, infestations are difficult to remove. New Mexico 

Watch List species. 
Pink, Rose, Red, or Purple Flowered Forbs

103

Meadow knapweed flower head

© CR

Meadow knapweed flower 

head

© EC

Meadow knapweed plant (left)

© CR

Meadow knapweed infestation 

(below)

© EC
104

Musk Thistle

Carduus nutans L. (Aster family, Asteraceae)

Description

Erect, single-stemmed annual or biennial forb; 1 to 7 feet tall; 

often forming dense patches; stems glabrous to wooly, spiny-winged 

from leaf bases; taprooted.

Leaves: Basal and cauline, alternate, lance-linear to elliptic, 4 to 

16 inches long, 1/4 to 8 inches wide; upper blades smaller, surfaces 

glabrous above, undersides furry—primarily along main veins, 

margins 1 to 2 pinnately lobed and spiny-toothed; basal leaves taper 

to winged petioles while cauline leaves are sessile.

Flowers: Flowers June to September; purple flower heads 

spherical 3/4 to 2-3/4 inches in diameter, nodding, solitary on stalks 

more than 3/4 inch long; flower head bracts glabrous to sparsely 

wooly, tips erect to spreading; flower head receptacles flat, densely 

covered with cream-colored bristles.

Fruits: Glossy golden to brown achenes elliptic, greater than 1/8 

inch long; curved, slightly compressed; cream-colored, 1/2 to 1 inch 

long, pappus bristles are numerous; united at the base to form a ring, 

and are deciduous as a unit.

Habitat

Moist cultivated and disturbed or degraded sites in meadows, 

grassland, chaparral, woodland, forest, and riparian communities, 

and roadsides within elevations that generally range from 4,200 to 

8,100 feet.

Propagation/Phenology

Plants appear to require a period of chilling to induce flowering; 

first flower heads can produce large numbers of seeds, sometimes 

1,500 or more seeds per head; later flower heads produce fewer 

seeds. Most seeds are dispersed within 165 feet of the parent plant; 

typically, seeds are dispersed 1 to 3 weeks after flowering. Seeds 

typically germinate during the winter/spring months and exist as a 

rosette until flowering in the spring/summer of the following year.
Pink, Rose, Red, or Purple Flowered Forbs

105

Musk thistle flower heads

© RL

Musk thistle basal rosette

© LTK

Comments

Native to Europe; serious infestations are often associated 

with sandy, fertile soils. This species and spiny plumeless 

thistle readily hybridize with one another, and plants with 

intermediate characteristics may be found where their ranges 

overlap. New Mexico Class B noxious weed and Oklahoma 

noxious weed.

Musk thistle flower heads

© SD

Musk thistle stems and 

foliage (above)

© MEH
106

Purple Loosestrife

Lythrum salicaria L. (Loosestrife family, Lythraceae) 

Description

Erect, single- or multi-stemmed, clump or patch-forming 

perennial forb or subshrub; 6 to 8 feet tall, taprooted; rose-purple 

flowers are showy; flowers are borne on elongated dense or open 

raceme, with an erect or drooping tip. 

Leaves: Stems are typically covered with short hairs; leaves 

lanceolate, 2 to 5-1/2 inches long; bases slightly lobed (cordate), 

covered with short hairs or glabrous, mostly opposite or whorled; 

upper leaves sometimes alternate.

Flowers: Flowers June to September; flowers showy, bright 

pinkish-purple, with 5 to 7 rough margined petals, 3/8 to 9/16 inch 

long; ovary superior but appears inferior, surrounded by and not 

fused to calyx tube.

Fruit: Capsules oblong-ovoid, 3/16-1/4 inch long, surrounded 

by persistent calyx tube, open into halves at tip; seeds numerous, 

reddish-brown, flattened, sometimes 3-angled in cross-section, often 

concave on 1 side, less than 1/16 inch long.

Habitat

Cultivated and disturbed or degraded sites in perennial and 

seasonal wetlands, including marsh and pond edges, streambanks, 

canals, and ditches; within elevations that generally range from 4,500 

to 6,800 feet.

Propagation/Phenology

Reproduces primarily by seed; however, stem fragments can 

develop roots under favorable conditions; large plants can produce 

more than 2 million viable seeds in one season; seedlings can mature 

and flower within 8 to 10 weeks.

Comments

Native to Europe; plants often form dense colonies that displace 

native vegetation and wildlife. Arizona prohibited noxious weed, 

New Mexico Class A noxious weed, and Texas noxious plant.
Pink, Rose, Red, or Purple Flowered Forbs

107

Purple loosestrife flowers

© NER

Purple loosestrife flowering 

inflorescence

© EC

Purple loosestrife foliage

© SD

Purple loosestrife plants (above)

© SD
108

Purple Starthistle

Centaurea calcitrapa L. (Aster family, Asteraceae)

Description

Multi-branched annual, biennial or perennial forb; 3 feet tall, 

with spiny or comb-like flower head bracts; stoutly taprooted plants 

exist as basal rosettes until erect, highly branched flowering stems 

are produced in late spring/summer. 

Leaves: Cotyledons spatulate to oval; rosette leaves pinnatedivided with straw-colored spines at their centers; leaves alternate, 

resin-dotted, lower stem leaves deeply 1 to 2 pinnate-lobed, 4 to 8 

inches long; upper stem leaves wingless, mostly pinnate-divided, 3/8 

to 3/4 inch long. Foliage variously covered with short to medium 

interwoven gray hairs; new leaves densely covered with gray hairs. 

Flowers: Flowers July to October; 1/4 to 3/8 inch diameter 

flower heads solitary or several with 25 to 40 purple flowers per 

head, 5/8 to 1 inch long; greenish or straw-colored flower head bracts 

overlapping in several rows, 5/8 to 3/4 inch long, tips variously spiny 

or comb-like; central spine stout, 3/8 to 1 inch long.

Fruit: White achenes oblong, 1/8 to 3/16 inch long, often brown 

streaked, apex flattened and tapered to a rounded, laterally notched 

base, often brown-streaked; pappus usually lacking.

Habitat

Cultivated and disturbed or degraded fertile soil sites in 

meadows, grassland, woodland, and forest communities, and 

roadsides within elevations that generally range from 3,300 to 8,000 

feet.

Propagation/Phenology

Reproduces by seed, up to 40,000 per plant; germination occurs 

over a broad range of environmental conditions; plants produce 

fewer viable seeds in dry years; infestation density correlates with 

the age of the population and degree of disturbance; plants seldom 

persist in shaded places.

Comments

Native to southern Europe; purple starthistle is a very 

competitive and aggressive plant with allelopathic effects; stands of 

purple starthistle may persist indefinitely once established. Arizona 
Pink, Rose, Red, or Purple Flowered Forbs

109

Purple starthistle 

flower head (left)

© BR

Purple starthistle flower 

head spines (right)

© BR

Purple 

starthistle 

plants (left)

© BR

Purple starthistle 

basal rosette 

(right)

© SD
110

Red Clover

Trifolium pratense L. (Pea family, Fabaceae)

Description

Red clover is a cool-season biennial or short-lived perennial with 

a number of leafy erect or ascending stems arising from the woody 

root crown, 4 to 8 inches long. Leaves and stems are pubescent. 

Plants have hollow, hairy stems and branches.

Leaves: The alternate leaves are composed of three leaflets 

(trifoliate), which may or may not have a “crescent” or “watermark” 

on the upper surface; stipules ovate, conspicuously veined, 3/8 to 

15/16 inch long; leaf stalks long; leaflets obovate or oval, 3/4 to 2 

inches long, entire or finely toothed; flowering heads sessile.

Flowers: Flowers June to October; the flower heads, each 

consisting of 40 to 100 or more flowers, are borne in compact 

clusters or heads; flowers rose-pink to purple; flower stalks to 1-3/16 

inches long; flower heads spherical, 7/8 to 1-3/8 inches in diameter; 

flower stems less than 1/8 inch long; flowers 1/2 to 3/4 inch long; 

calyx 5/16 to 1-1/32 inches long, hairy; corolla 13/32 to 13/16 inch 

long, rose-pink to purple.

Fruit: The fruit is a legume, less than 3/16 inch long, with 1 to 

2 kidney-shaped seeds that vary in color from yellow to deep violet; 

produces roughly 272,000 seeds per pound.

Habitat

Red clover grows best on well drained loam soil, in wet to 

dry meadows, open forests, and forest margins within elevations that 

are generally below 8,500 feet.

Propagation/Phenology

Reproduces by seed.

Comments

Native to Europe; red clover has an extensively branched and 

deeply penetrating (8 feet or more) taproot and makes its best growth 

on rich, deep, well-drained soil. Red clover may become weedy 

or invasive in some regions or habitats and may displace desirable 

vegetation if not properly managed, making it a concern in 
Pink, Rose, Red, or Purple Flowered Forbs

111

riparian and moist meadow habitats. This species generally 

occurs as a weed in wildland areas of the Southwestern Region 

rather than as an invasive plant.

Red clover flowers and foliage

© F&KS

Red clover plants

© TH

Red clover flowers 

and foliage

© JM

Red clover 

trifoliate leaves

© RO
112

Redstem Filaree

Erodium cicutarium (L.) L’Hér. ex Ait. 

(Geranium family, Geraniaceae)

Description

Spreading or erect, winter annual or biennial forb, 4 to 24 inches 

long, generally from a basal rosette; covered with partially glandular 

hairs; stems are often tinted red in color; small taproot with a fibrous 

root system; it often carpets large areas.

Leaves: Basal rosette leaves are up to 8 inches long and 2-1/2 

inches across; odd-pinnate and have long petioles; both the central 

stalk of these compound leaves and their petioles are reddish green 

or reddish brown and covered with long white hairs, like the stems; 

hairy leaflets are up to 1 inch long and 1/2 inch wide, pinnately cleft 

with both shallow and deep lobes, margins ciliate; cauline leaves 

similar basal leaves, but smaller in size with shorter petioles; base 

of each cauline leaf, there is a pair of small stipules that are ovate in 

shape.

Flowers: Flowers February to May; stems bear 2 to 8 bright 

pink to purple, 5-petalled flowers, 1/2 inch wide, arranged in loose 

cluster of 2 to 12, usually with dark spots on the bases; each flower 

occurring on a relatively long flower stalk up to 1 foot tall.

Fruit: Each flower develops into a seed capsule in the form of 

a long narrow beak (stork’s bill) up to 2 inches long; at maturity, 

capsule splits apart into 5 narrow linear segments; each segment has 

a single seed at the bottom; seed linear in shape, somewhat broader 

at the top and tapering to a point at the bottom; as the attached 

segment dries, it forms an irregular spiral that can drill the seed into 

the ground.

Habitat

Cultivated and disturbed or degraded sites in meadows, grassland 

and woodland communities, and roadsides; it grows in well-drained, 

clayey, loamy, or sandy soil within elevations that generally range 

from 3,000 to 8,100 feet.

Propagation/Phenology

Reproduces by seed; some estimates of total seed produced per 

plant are more than 5,000.
Pink, Rose, Red, or Purple Flowered Forbs

113

Redstem filaree 

flowers and fruit 

(right)

© BM

Redstem filaree flowers and foliage 

(left)

© RO

Comments

Native to Europe; redstem filaree colonizes easily and 

quickly forms dense monocultures on disturbed habitats. This 

species generally occurs as a weed in wildland areas of the 

Southwestern Region rather than as an invasive plant.

Redstem filaree flowers and foliage 

(below)

© JB

Redstem filaree plants 

(left)

© F&KS
114

Russian Knapweed

Acroptilon repens (L.) DC (Aster family, Asteraceae)

Description

Multi-stemmed perennial forb, 9 to 39 inches tall; openly 

branched stems covered with cobwebby, matted hairs; creeping 

rhizomes scaly, dark brown to black; root system branches frequently 

with individual roots reaching 25 feet in depth; stems with numerous 

branches; Russian knapweed is similar in appearance to other 

knapweeds and star-thistles; however, Russian knapweed has 

rounded to pointed membranous margins whereas flower head bracts 

of other knapweeds and star-thistles are tipped or fringed with short 

spines.

Leaves: Basal and cauline (along the stem), simple, alternate; 

upper cauline leaves narrowly lanceolate to linear, 1/8 to 1/2 inch 

long, margins entire or toothed; lower cauline leaves often serrate; 

basal leaves lobed and gray pubescent.

Flowers: Flowers June to September; pink to purplish flower 

heads range from one to numerous, rising at the end of branches, 

arranged in a flat-topped to panicle-like inflorescence; flower head 

bracts arranged in 6 to 8 rows.

Fruits: Oblong achene (fruit), 1/8 to 1/4 inch long; deciduous 

pappus (tuft-like appendage) at end of achene, whitish bristles 

unequal, 1/8 to 3/8 inch long, barbed toward the base, feathery 

toward the tip.

Habitat

Cultivated areas and disturbed or degraded sites in meadows, 

grassland and riparian communities, and roadsides; establishes in 

many soil types within elevations that generally range from 3,000 to 

8,000 feet.

Propagation/Phenology

Reproduces primarily by vegetative shoots from rhizomes 

although individual plants can produce small quantities of viable 

seed. Seed can remain viable 2 to 3 years. Severed roots can produce 

new shoots from a depth of up to 6 inches.
Pink, Rose, Red, or Purple Flowered Forbs

115

Russian knapweed flower heads

© SD

Russian knapweed flower heads 

and foliage (above)

© JMR

Russian knapweed 

foliage (right)

© BM

Comments

Native to central Asia; Russian knapweed is a very 

competitive and aggressive plant with allelopathic effects; 

stands may persist indefinitely once established. Arizona 

prohibited/restricted noxious weed and New Mexico Class B 

noxious weed.

Russian knapweed 

plants (left)

© SD
116

Scotch Thistle

Onopordum acanthium L. (Aster family, Asteraceae)

Description

Vigorous biennial or short-lived warm-season perennial forb with 

coarse, spiny leaves and conspicuous spiny-winged stems; 1-1/2 to 12 feet 

tall. 

Leaves: Stems wings, spiny, continuous, and conspicuous, 3/4 to 

1-1/4 inches wide; leaves alternate, spiny; leaves covered with gray-white 

woolly hairs, with the lower surface more densely covered than the upper; 

leaves 4 to 20 inches long, broadly elliptic; margins spiny-toothed to 

shallow spiny-lobed.

Flowers: Flowers June to September; flower heads are numerous 

mostly solitary but sometimes in clusters of 2 to 7, 1 to 2 inches in 

diameter, flowers white to purple; flower head bracts spine-tipped, less 

than 1/8 inch. 

Fruit: Achenes narrowly obovate, more or less 4- or 5-angled, 

glabrous, and mottled brown to blackish; surface roughened with wavy 

transverse ridges, less than 1/8 inch long; pink to reddish pappus bristles 

equal, numerous, minutely barbed, fused into a ring at the base which 

separates as a unit, 5/16 to 7/16 inch long.

Habitat

Cultivated and disturbed or degraded moist sites in meadows, 

grassland, woodland, and riparian communities, and roadsides; within 

elevations that generally range below 7,500 feet.

Propagation/Phenology

Reproduces only by seed; plants can produce an average of 20,000 to 

40,000 seeds; most seeds germinate in fall after the first rains, but some 

seeds can germinate year round under favorable moisture and temperature 

conditions; buried seed can remain viable in the soil seed bank for at least 

7 years and possibly to 20 years or more; yearly seed production and seed 

dormancy are highly variable depending on environmental conditions.

Comments

Native to Europe and the Mediterranean region; severe infestations 

can form tall, dense, impenetrable stands, especially in fertile soils. 

Arizona prohibited/restricted noxious weed, New Mexico Class A noxious 

weed, and Oklahoma noxious weed.
Pink, Rose, Red, or Purple Flowered Forbs

117

Scotch thistle flower heads

© SD

Scotch thistle flower head and 

winged stems (left)

© BM

Scotch thistle foliage

© RV

Scotch thistle 

plant (right)

© SD
118

Spiny Plumeless Thistle

Carduus acanthoides L. (Aster family, Asteraceae)

Description

Multi-stemmed biennial (or winter annual) forb to 5 feet 

tall; openly branched stems erect, spiny-winged from leaf bases; 

taprooted; plants exist as basal rosettes until flowering shoots 

develop at maturity.

Leaves: Basal leaves opposite, elliptic to lanceolate, pinnately 

lobed, with prickly-toothed margins; stem leaves alternate, with 

bases that extend down the stem forming spiny wings (decurrent); 

stems strongly winged, glabrous to lightly woolly; leaves 1-pinnate 

lobed, typically sparsely hairy, lower leaves mostly 4 to 8 inches 

long.

Flowers: Flowers May to August; purple flower heads spherical 

3/8 to 1-1/8 inches in diameter, one to numerous on stalks less than 

3/4 inch long; flower head bracts glabrous to pubescent, tips erect to 

spreading; flower head receptacles flat, densely covered with creamcolored bristles.

Fruits: Glossy golden to brown achenes elliptic, less than 1/8 

inch long; curved, slightly compressed; cream-colored, 3/8 to 1/2 

inch long, pappus bristles are numerous; united at the base to form a 

ring and are deciduous as a unit.

Habitat

Dry, well drained, cultivated and disturbed or degraded sites 

in meadows, grassland, chaparral, woodland, forest, and riparian 

communities, and roadsides within elevations that generally range 

from 4,200 to 8,800 feet.

Propagation/Phenology

Reproduces by seed; seeds appear to lack an after ripening 

period. Seeds typically germinate late summer through spring, 

depending on environmental conditions. Seeds can germinate in 

constant heavy shade, but seedlings seldom reach maturity under this 

condition; additionally, viable seeds rarely persist in the soil seed 

bank due to decomposition and seed predation by insects, mammals, 

and birds.
Pink, Rose, Red, or Purple Flowered Forbs

119

Spiny plumeless thistle flower 

heads

© GLP

Spiny plumeless thistle flower 

heads, winged stems, and foliage

© TP

Comments

Native to Europe; serious infestations are often associated 

with sandy, fertile soils; this species and musk thistle readily 

hybridize with one another, and plants with intermediate 

characteristics may be found where their ranges overlap. 

Arizona prohibited noxious weed. 

Spiny plumeless thistle basal 

rosette

© TP

Spiny plumeless thistle 

plants (above)

© TP
120

Spotted Knapweed

Centaurea stoebe L. ssp. micranthos (Gugler) 

Hayek (Aster family, Asteraceae)

Description

Multi-branched biennial or short-lived perennial forb, 39 inches 

tall, with spiny or comb-like flower head bracts; stoutly taprooted; 

plants exist as basal rosettes until erect, highly branched flowering 

stems are produced in late spring/summer.

Leaves: Cotyledons spatulate to oval; rosette leaves pinnatedivided without straw-colored spines at their centers; leaves alternate, 

resin-dotted, lower stem leaves deeply 1 to 2 pinnate-lobed, 4 to 8 

inches long; upper stem leaves wingless, mostly pinnate-divided, 3/8 

to 3/4 inch long. Foliage variously covered with short to medium 

interwoven gray hairs; new leaves green and covered with minute 

bristly hairs.

Flowers: Flowers June to October; 1/4 to 1/2 inch diameter 

flower heads, solitary or several with 30 to 40 white, pink or purple 

flowers per head, 1/2 to 1 inch long; pale green or pink-tinged flower 

head bracts overlapping in several rows, 5/8 to 3/4 inch long, tips 

dark, comb-like, not spine-tipped.

Fruit: Pale brown achenes oblong, 1/8 to 3/16 inch long, finely 

hairy, apex flattened and tapered to a rounded, laterally notched base; 

pappus bristles less than 1/8 inch long.

Habitat

Cultivated and disturbed or degraded sites in meadows and 

grasslands within elevations that generally range below 7,000 feet.

Propagation/Phenology

Reproduces by seed, up to 40,000 per plant; germination occurs 

over a broad range of environmental conditions; in addition to seeds, 

spotted knapweed can reproduce vegetatively from lateral roots just 

below the soil surface.

Comments

Native to Europe; spotted knapweed is a very competitive and 

aggressive plant with allelopathic effects; stands of spotted knapweed 

may persist indefinitely once established. Arizona prohibited/restricted 

noxious weed and New Mexico Class A noxious weed. 
Pink, Rose, Red, or Purple Flowered Forbs

121

Spotted knapweed 

foliage (right)

© OSWL

Spotted knapweed flower head

© JC

Spotted knapweed dried bracts 

and flower heads (below)

© SD

Spotted knapweed plants (above) 

© SD
122

Squarrose Knapweed

Centaurea virgata Lam. ssp. squarrosa (Willd.) 

Gugler (Aster family, Asteraceae)

Description

Erect, multi-branched perennial forb with a woody base, 20 inches 

tall, with spiny or comb-like flower head bracts; stoutly taprooted; 

plants exist as basal rosettes until erect, highly branched flowering 

stems are produced in late spring/summer.

Leaves: Cotyledons spatulate to oval; rosette leaves pinnatedivided; leaves resin-dotted; upper stem leaves entire, linear or bractlike, mostly lacking at flowering, 3/8 to 3/4 inch long.

Flowers: Flowers June to August; flower heads solitary or several; 

pink to pale purple flowers average 4 to 8 per head, 1/4 to 3/8 inch 

long; flower head bracts roughly 1/4 inch long, pale green to straw 

colored sometimes purple-tinged, spine-tipped; central spine usually 

reflexed downward to 1/8 inch long. 

Fruit: Pale brown achenes oblong, 1/8 to 3/16 inch long, apex 

flattened and tapered to a rounded, laterally notched base, finely hairy, 

roughly 2 to 4 per head, pappus bristles less than 1/8 inch long or 

lacking.

Habitat

Cultivated and disturbed or degraded rangelands and roadsides 

within elevations that generally range below 8,000 feet.

Propagation/Phenology

Reproduces by seed, germination can occur over a broad range 

of environmental conditions; seedling emergence is typically highest 

after the first fall rains; mortality of seedlings that emerge in spring 

can be high when conditions become dry after emergence; most 

seedlings emerge from seeds at or near the soil surface; plants produce 

fewer viable seeds in dry years; infestation density correlates with the 

age of the population and degree of disturbance.

Comments

Native to Asia; squarrose knapweed is a very competitive 

and aggressive plant with allelopathic effects; stands of squarrose 

knapweed may persist indefinitely once established. Arizona 

prohibited noxious weed.
Pink, Rose, Red, or Purple Flowered Forbs

123

Squarrose knapweed 

flower heads (left)

© SD

Squarrose 

knapweed 

flower heads 

(right)

© SD

Squarrose 

knapweed 

foliage (right)

© JMD

Squarrose knapweed plants (above)

© SD
124

Tall Morning-glory

Ipomoea purpurea (L.) Roth

 (Morning-glory family, Convolvulaceae)

Description

Tall morning-glory is a warm-season trailing or climbing annual 

vine, capable of reaching 6-1/2 feet in length. The stems twine in a 

dextral (having the whorls coiling clockwise) fashion.

Leaves: Leaves are often heart shaped, sometimes three lobed 

(both leaf types can occur on the same plant); from 3/8 to 4-5/16 

inches long and 3/8 to 4-3/4 inches wide; alternate along the stem; 

minute flattened hairs usually cover the leaf surface, but sometimes 

leaves are nearly hairless; petioles range from 3/8 to 5-1/2 inches 

long.

Flowers: Flowers June to November; flowers grow singly or in 

clusters of two to five showy, funnel-shaped, stalked, purple, blue, 

pink, white, or bi-colored; 1 to 3 inches long by 1 to 2 inches wide; 

sepals at the base of the flower approximately 3/8 to 5/8 inch long.

Fruit: The fruit is a subglobose to ovoid dark brown to black 

capsule that is approximately 3/8 inch in diameter and up to 1 inch 

long; contains 3 to 6 wedge-shaped seeds, 3/16 to 5/16 inch long, dull 

with a granular surface. 

Habitat

Cultivated and disturbed or degraded sites in moist meadows and 

riparian communities, and roadsides within elevations that generally 

range from below 7,500 feet.

Propagation/Phenology

Reproduces by seed; one plant can produce up to 26,000 seeds; 

germinating at depths of 4 inches or more, much deeper than most 

annuals.

Comments

Native to Central America; once established, tall morning-glory 

is difficult to control. Arizona prohibited noxious weed.
Pink, Rose, Red, or Purple Flowered Forbs

125

Tall morning-glory 

funnel shaped flower

© PJA

Tall morning-glory flowers 

and foliage

© JHM&TB

Tall morning-glory flower and foliage

© PTL

Tall morning-glory flowers 

and foliage (both heartshaped and lobed leaves)

© RRB
126

Teasel

Dipsacus fullonum L. (Teasel family, Dipsacaceae)

Description

Erect, stout, biennial forb, 3 to 6 feet tall; stem striate, angled, 

prickly on the angles and becoming more so upward; large taproot.

Leaves: Basal and stem leaves opposite, simple, blades may be 

prickly, especially on the midnerve below, otherwise glabrous; basal 

leaves oblong to oblanceolate, margins crenate, apex obtuse to acute; 

cauline leaves 1/2 to 1-1/4 inches long, the lower blades crenate to 

serrate, becoming entire upward, often ciliate; stem leaves are perfoliate 

(each pair of opposite leaves is joined at the point where they attach to 

the stem, giving the appearance of a single leaf pierced by the stem).

Flowers: Flowers July to October; inflorescence an erect, 

flower heads are ovoid to cylindrical, 1-1/4 to 4 inches long, flowers 

numerous; peduncles long, prickly; flower head bracts curving upward, 

linear, elongate, unequal, the longer ones often surpassing the heads; 

prickly, the apex spine-tipped; bracts of the receptacle tapering to 

an acuminate, stout, straight awn that surpasses the flowers; slender 

flowers lavender, pale purple or sometimes white, 4-lobed, 1/2 to 3/4 

inch long.

Fruit: Achenes 1/4 inch long, 4-angled and appressed-hairy.

Habitat

Cultivated and disturbed or degraded sites in moist meadows and 

riparian communities, and roadsides within elevations that generally 

range from 4,700 to 8,700 feet.

Propagation/Phenology

A single teasel plant can produce over 2,000 seeds; up to 30 to 80 

percent of the seeds may germinate or may remain viable for at least 2 

years; typically seeds do not disperse far; most seedlings will be located 

near the parent plant.

Comments

Native to Europe; teasel flowers open in an unusual pattern; a band 

of flowers opens first around the middle of the head, then the blooms 

progress both up and down and eventually form two bands; the fusion 

of the two leaf bases at the stem forms something of a “cup” that 

catches and holds rainwater. New Mexico Class B noxious weed.
Pink, Rose, Red, or Purple Flowered Forbs

127

Teasel basal 

rosettes

© SD

Teasel stem and 

leaf arrangement

© BR

Teasel flower head

© LR

Teasel flower heads, stems, and 

foliage (below) 

© LR
128
Violet Flowered Forbs

129

Carolina horsenettle © OSWL
130

Bigleaf Periwinkle

Vinca major L. (Dogbane family, Apocynaceae)

Description

Bigleaf periwinkle is a perennial, deep-rooted vine with nonflowering, scrambling, or trailing stolons up to 3 feet long and 

flowering vertical stems 1-1/2 feet high. The succulent stems, with 

milky juice, are dark green and become somewhat woody at the 

caudex.

Leaves: Leaves are semi-evergreen, in pairs opposite each 

other along the stems, have a waxy cuticle, and are heart shaped to 

triangular, 1-1/2 to 3 inches long.

Flowers: Flowers March to June; flowers solitary in the leaf axils, 

on long pedicels; calyx divided nearly to the base, the 5 lobes linear, 

with short bristles on the margins; corolla purplish-blue, with long, 

narrow tube and 5 widely spreading, truncate lobes, 1-1/8 to 2 inches 

wide; corolla tube about 3/4 inch long, crested and hairy in the throat.

Fruit: Fruits are slender, cylindrical follicles up to 2 inches long; 

follicles dry, split, and release 3 to 5 seeds.

Habitat

Bigleaf periwinkle occurs in riparian areas, forests, and grasslands; 

it is also associated with sites linked to human activities, including old 

homesteads, roadsides, waste places, and other highly disturbed areas, 

within elevations that generally range below 7,500 feet.

Propagation/Phenology

Reproduces primarily by vegetative regeneration and limited 

seeding.

Comments

Native to Mediterranean Europe, Asia Minor, and northern Africa; 

bigleaf periwinkle is most problematic to managers in riparian or 

canyon bottom habitats. The tendency of bigleaf periwinkle to form 

dense mats under woody canopies may lead to the exclusion of native 

species. This species generally occurs as a weed in wildland areas of 

the Southwestern Region rather than as an invasive plant. 
Violet Flowered Forbs

131

Bigleaf periwinkle flower and foliage

© LR

Bigleaf periwinkle flower 

and foliage

© ML

Bigleaf periwinkle foliage

© LR

Bigleaf periwinkle flower

© LR
132

Carolina Horsenettle

Solanum carolinense L. (Potato family, Solanaceae)

Description

Erect to sprawling perennial herb to subshrub with deep creeping 

roots, and yellowish prickles on the stems, to 39 inches tall.

Leaves: Stems usually prickly, openly branched; leaves are 

alternate, simple, dull green, ovate to lanceolate, 2 to 6 inches long, 

usually with wavy to 5 to 7 coarse-lobed margins; foliage is covered 

with minute star-shaped hairs, typically yellowish to straw-colored.

Flowers: Flowers May to September; flower clusters are 

modified cymes that are raceme-like, with 5 to 20 pale violet or 

white star-shaped, 5-lobed flowers, 3/4 to 1-1/8 inches in diameter.

Fruit: Fruit is a yellow 5/16 to 3/4 inch diameter berry with 40 

to 170 seeds; seeds are yellowish to orange-brown; small 1/16 to 1/8 

inch in diameter; smooth and glossy.

Habitat

Cultivated and disturbed or degraded sites in grassland and 

woodland communities, and roadsides; grows best on sandy, welldrained soils within elevations that generally range from 4,000 to 

5,000 feet.

Propagation/Phenology

Reproduces by seed and vegetatively from creeping roots and 

root fragments; one plant can produce up to 5,000 seeds; most seed 

is dormant at maturity and requires a cool, moist period to germinate 

spring through summer; roots generate new shoots in spring.

Comments

Native to the central and eastern United States and northern 

Mexico; once established, Carolina horsenettle colonies are difficult 

to control or eliminate. Arizona prohibited noxious weed.
Violet Flowered Forbs

133

Carolina 

horsenettle 

flowers

© OSWL

Carolina 

horsenettle 

flowers and 

foliage

© TB

Carolina 

horsenettle 

fruit and 

stem

© TB

Carolina 

horsenettle 

plant

© OSWL
134

Chicory

Cichorium intybus L. (Aster family, Asteraceae)

Description

Chicory is a deeply rooted erect, branching, biennial or 

perennial, warm-season forb, from 1 to 6 feet tall with milky sap. 

Basal rosette of leaves arise from a long fleshy taproot. Stem color is 

green or reddish.

Leaves: Basal leaves in rosette; basal and cauline leaves are 

alternate, clasping, and hairy, 2 to 10 inches long and 1/2 to 2-3/4 

inches wide; basal leaves spatulate in outline, irregularly saw toothed 

or pinnately incised, with the lobes or teeth hooked backward; stem 

leaves become reduced, sessile, entire to toothed.

Flowers: Flowers June to August; blue, rarely white or pink, 

flower heads are relatively large, 1 to 1-9/16 inches in diameter, 

borne in widely spaced sessile clusters (1 to 3) along the branches 

or at the apex of short branches; ray flowers are blunt and 5 toothed 

at the apex. Involucre 3/8 to 5/8 inch high, the bracts in two series, 

the outer about half as long as the inner; pappus of narrow, minute 

scales.

Fruit: Achenes weakly 5-angled, 1/16 to 1/8 inch long, tipped 

with a crown of minute scales. 

Habitat

Waste places and disturbed sites, especially along roadsides 

typically within elevations that generally range from 4,000 to 8,000 

feet.

Propagation/Phenology

Reproduces by seed; can produce as many as 425,000 seeds per 

pound.

Comments

Native to southern and central Europe and western Asia; chicory 

has beautiful flowers and a very attractive growth habit; however, 

it is a good example of a nonnative species that remains sparsely 

scattered during early population establishment and then within a 

few years can show up in masses far and wide; New Mexico Class B 

noxious weed.
Violet Flowered Forbs

135

Chicory plant 

basal foliage

© RV

Chicory plant(s) 

flowering stems 

and foliage

© RAH

Chicory flower head 

and foliage

© AV

Chicory flower head

© BR
136
White Flowered Forbs

137

Oxeye daisy © MEH
138

African Rue

Peganum harmala L. (Creosote-bush family, Zygophyllaceae)

Description

Bushy, much-branched perennial forb with short creeping roots 

to 32 inches tall; stems stiff, erect, branches angled above, glabrous.

Leaves: Leaves are alternate, fleshy, bright green, 3/4 to 2 

inches long, irregularly divided 3 times or more into linear segments; 

stipules bristle-like.

Flowers: Flowers April to September; flowers have 5 white 

petals, about 1 inch in diameter and solitary on stalks 3/4 to 2 inches 

long or more in the leaf axils; the 5 sepals are linear, about 9/16 inch 

long; the 5 petals are oblong, also about 9/16 inch long.

Fruit: Capsules spherical, leathery, 5/16 to 9/16 inch in 

diameter, orange-brown at maturity; 3-chambered, and opening by 3 

valves at the apex to release numerous dark brown to black angular 

seeds, 1/8 to 3/16 inch long.

Habitat

Cultivated and disturbed or degraded dry open sites in meadows 

and grassland communities, and roadsides within elevations that 

generally range below 4,500 feet.

Propagation/Phenology

Reproduces primarily by seed, but roots can produce new shoots, 

especially when severed; most seed falls near the parent plant; seeds 

can germinate under fairly saline conditions.

Comments

Native to the Mediterranean region and Middle East; heavy 

infestations of African rue are difficult to control. Arizona prohibited 

noxious weed and New Mexico Class B noxious weed.
White Flowered Forbs

139

African rue 

plants in 

flower

© GAC

African rue flower

© GAC

African rue fruit 

and leaves 

© DB

African rue 

foliage

© JMT
140

Broadleaved Pepperweed

Lepidium latifolium L. (Mustard family, Brassicaceae)

Description

Erect perennial forb 1 to 6-1/2 feet tall, with white flowers and 

extensively creeping roots; plants are highly competitive and typically 

form dense colonies that displace native vegetation.

Leaves: Root crown and lower stems weakly woody; bright green 

to gray-green foliage is glabrous; leaves are alternate, lanceolate to 

elliptic or oblong in shape; basal leaves to 12 inches long and 3-3/16 

inches wide, with serrate margins and on long stalks 1-3/16 to 5-7/8 

inches long; stem leaves reduced, sessile, tapered at the base, margins 

entire to weakly serrate.

Flowers: Flowers May to September; flowering inflorescences 

pyramidal to rounded on top; 4 spoon-shaped petalled flowers are white 

and in dense clusters; less than 1/16 inch long; sepals oval, also less 

than 1/16 inch long, covered with long simple hairs; stamens 6, 4 long 

and 2 short.

Fruit: Pods (silicles), 2-chambered, round to slightly ovate, slightly 

flattened, lacking a notch at the apex, 1/16 inch long, covered with long 

simple hairs; stigma sessile, persistent with the pod; stalks much longer 

than pods, glabrous or sparsely pubescent; seeds 2 per fruit, ellipsoid, 

slightly flattened, less than 1/16 inch long or wide; reddish-brown, with 

a shallow groove on each side and minutely granular surface.

Habitat

Cultivated and disturbed or degraded moist open sites in meadows, 

grassland, woodland, forest, and riparian communities, and roadsides 

within elevations that generally range from 4,100 to 7,900 feet.

Propagation/Phenology

Reproduces vegetatively from vigorously creeping long, thick 

roots, root fragments and by seed; plants usually produce abundant, 

often highly viable seed.

Comments

Native to Eurasia; heavy infestations of broadleaved pepperweed 

are difficult to control; roots do not hold soil together very well, 

allowing erosion of riverbanks and streambanks. New Mexico Class B 

noxious weed. 
White Flowered Forbs

141

Broadleaved 

pepperweed 

flowers (left)

© MEH

Broadleaved 

pepperweed 

foliage

© PTL

Broadleaved 

pepperweed 

plants (right)

© SD

Broadleaved pepperweed roots

© SD
142

Field Bindweed

Convolvulus arvensis L. 

(Morning-glory family, Convolvulaceae)

Description 

Vine-like perennial forb, 1 to 4 feet long, with an extensive 

system of deep creeping roots and rhizomes; stems twine around 

and over other plants or trail along the ground, often forming dense 

tangled mats; roots are cord-like, white, fleshy and brittle.

Leaves: Leaves are alternate, simple, short-stalked, arrowheadshaped to oblong or round, tips often rounded, typically 3/4 to 1 inch 

long and 3/8 to 1-3/8 inches wide, glabrous or sparsely covered with 

short hairs, dull green, sometimes covered with a whitish powdery 

bloom; basal lobes more or less pointed, often flared outward; leaf 

size and shape vary greatly depending on environmental conditions 

such as light intensity, soil moisture, and frequency of defoliation.

Flowers: Flowers April to October; flowers axillary, solitary 

or in cymes of 2 to 4, on stalks 3/4 to 2-3/8 inches long; white or 

pinkish corollas funnel-shaped, 9/16 to 1-3/16 inches long, pleated 

and spiraled in bud; calyx bell-shaped, usually less than 3/16 inch 

long; flowers open for 1 day.

Fruit: Capsules spherical, inflated, 5/16 inch in diameter; seeds 

few per capsule, variable in shape, but typically obovate, slightly 

compressed, more less 3-sided in cross-section, less than 3/16 inch 

long, dull dark gray-brown, covered with small, rough, irregular 

bumps.

Habitat

Cultivated and disturbed or degraded sites in grassland, 

chaparral, woodland, forest, and riparian communities, and roadsides 

within elevations that generally range from 3,500 to 10,000 feet.

Propagation/Phenology

Reproduces by seed and vegetatively from deep creeping roots 

and rhizomes; undisturbed patches can expand their radius up to 33 

feet per year; root fragments as small as 2 inches can generate new 

shoots.

Comments

Native to Europe; once established, field bindweed infestations 
White Flowered Forbs

143

Field bindweed 

plants in bloom 

(left)

© TH

Field bindweed 

plants

© MEH

are very difficult to control. Arizona prohibited/regulated 

noxious weed and Texas noxious plant.

Field bindweed flower, stem, 

and leaves (below)

© TH

Field bindweed foliage (left)

© MEH
144

Hairy Whitetop 

Cardaria pubescens (C. A. Mey) Jarmolenko 

(Mustard family, Brassicaceae)

Description

Multi-stemmed perennial forb, 18 to 20 inches tall; erect stems 

sparse to densely covered with simple short hairs; seed production 

is prolific; new shoots arise from buds on lateral roots or root 

fragments; establishes dense stands that exclude other vegetation.

Leaves: Gray-green, alternate, obovate, lanceolate, and oblong 

to elliptic; surfaces, especially lower, sparsely to densely covered 

with simple, short white hairs, margins irregularly toothed to entire; 

basal leaves short-stalked 3-1/2 inches long and 3/4 inch wide or 

less; sessile upper leaves are densely hairy with rounded to acutelobed bases that clasp the stem.

Flowers: Flowers April to October; inflorescences often flattopped; small (1/8 inch long), fragrant, white, 4-petaled flowers are 

numerous; sepals are covered with simple short hairs.

Fruits: Pods strongly inflated, spherical to ovoid in outline, 1/8 

to 5/16 inch long and wide, covered with short hairs; style persistent, 

1/16 to 1/8 inch long at the apex; seeds 1 to 2 per chamber, ovoid, 

slightly flattened, reddish-brown, less than 1/8 inch long and 1/16 

inch wide.

Habitat

Cultivated and disturbed or degraded moist sites in meadows, 

grassland, chaparral, woodland, forest, and riparian communities, 

and roadsides; generally grows on alkaline to saline soils, but 

tolerates many soil types and moisture conditions within elevations 

that generally range from 3,000 to 8,000 feet.

Propagation/Phenology

Reproduces vegetatively from creeping roots and less 

importantly by seed; this species is an aggressive weed; mature 

plants develop extensive systems of persistent, deep vertical and 

horizontal roots to depths of 6-1/2 feet or more; root fragments 

generate new plants, but regeneration is poor in dry soils.
White Flowered Forbs

145

Comments

Native to central Asia; this species is difficult to 

distinguish from lens-podded hoarycress and whitetop in 

the seedling and vegetative states; hairy whitetop competes 

poorly with shrubs in natural communities. Arizona prohibited 

noxious weed and New Mexico Class A noxious weed.

Hairy whitetop flowers, 

clasping leaves, and 

stems (left)

© JMT

Hairy whitetop 

fruit

© RO

Hairy whitetop 

plants

© JMT

Hairy whitetop 

clasping leaves and 

stem (left)

© MEH
146

Horehound

Marrubium vulgare L. (Mint family, Lamiaceae)

Description

Horehound is an upright bushy, cool-season, perennial forb or 

subshrub, 9 to 30 inches tall. It has dense, white woolly 4-angled 

stems branching from a somewhat woody base. Both the stems and 

leaves are very aromatic and have a bitter taste.

Leaves: The opposite leaves are petioled 3/16 to 1-15/16 inches 

long, round to oval in outline, corrugated (wrinkled), 9/16 to 1-15/16 

inch long and wide; pale green above and white woolly beneath, 

with coarsely-toothed margins.

Flowers: Flowers March to October; flowers small, white, 

tubular, 1/4 to 5/16 inch long, crowded into very dense, compact, 

round clusters around the stem in the leaf axil; flower clusters also 

occur at the ends of all the branches, and often extend for more than 

a foot on the stem; calyx is also tubular, with 10 spinelike teeth 

which curve downward and are hook tipped in age, calyx persistent, 

and encloses the 4-parted fruits.

Fruit: Fruit is a burlike, 4-parted nutlet, egg shaped, brown or 

dark gray, about 1/12 inch long, and somewhat 3-angled, surface has 

scattered dark granules; 1 seed per nutlet, less than 1/16 inch long.

Habitat

Cultivated and disturbed or degraded sites in deserts, uplands, 

mountains, and riparian habitats within elevations that generally 

range below 8,500 feet.

Propagation/Phenology

Reproduces by seed.

Comments

Native to Europe; although somewhat bitter and possessing a 

unique, pungent flavor, the fresh or dried leaves are edible and can 

be used as a seasoning or flavoring, made into pleasant tasting and 

medicinal tea. Horehound is often included in herbal cough drops. 

This species generally occurs as a weed in wildland areas of the 

Southwestern Region rather than as an invasive plant.
White Flowered Forbs

147

Horehound flowers 

and foliage

© PJA

Horehound 

flowers and 

foliage

© KAR

Horehound 

plant(s)

© LR

Horehound flowers and foliage

© PJA
148

Lens-podded Hoarycress

Cardaria chalepensis (L.) Hand.-Maz. 

(Mustard family, Brassicaceae)

Description

Multi-stemmed perennial forb (may take on the appearance of a 

shrub), 8 to 25-1/2 inches tall; seed production is prolific; new shoots 

arise from buds on lateral roots or root fragments; establishes dense 

stands that exclude other vegetation.

Leaves: Gray-green, alternate, obovate, lanceolate, and oblong 

to elliptic; surfaces, especially lower, sparsely to densely covered 

with short white hairs, margins irregularly toothed to entire; basal 

leaves short-stalked; upper leaves sessile, with rounded to acutelobed bases that clasp the stem, 3 inches long and 1 inch wide or 

smaller.

Flowers: Flowers April to August; inflorescences often flattopped; small (3/16 inch long), fragrant, white, 4-petaled flowers are 

numerous; sepals are glabrous. 

Fruits: Pods disc-shaped, round to broadly (ob)ovate or barely 

kidney-shaped in outline, 1/8 to 3/8 inch long, 1/8 to 1/4 inch wide, 

glabrous; style persistent, 1/16 to 1/8 inch long at the apex; seeds 1 to 

2 per chamber, ovoid, slightly flattened, reddish-brown, less than 1/8 

inch long and 1/16 inch wide.

Habitat

Cultivated and disturbed or degraded moist sites in meadows, 

grassland, chaparral, woodland, forest, and riparian communities, 

and roadsides; generally grows on alkaline to saline soils, but 

tolerates many soil types and moisture conditions within elevations 

that generally range from 3,300 to 6,000 feet.

Propagation/Phenology

Reproduces vegetatively from creeping roots and less 

importantly by seed. This species is an aggressive weed; mature 

plants develop extensive systems of persistent, deep vertical and 

horizontal roots to depths of 6-1/2 feet or more. Root fragments 

generate new plants, but regeneration is poor in dry soils.
White Flowered Forbs

149

Lens-podded hoarycress flowers 

(below)

© TNC

Lens-podded hoarycress fruit 

(below)

© JMD Lens-podded hoarycress plants

© MEH

Comments

Native to central Asia; this species is difficult to 

distinguish from hairy whitetop and whitetop in the seedling 

and vegetative states; lens-podded hoarycress competes 

poorly with shrubs in natural communities. Arizona prohibited 

noxious weed and New Mexico Class A noxious weed.

Lens-podded hoarycress plants

© SM
150

Onionweed

Asphodelus fistulosus L. (Lily family, Liliaceae)

Description

Onionweed is a tufted, dark green annual or short-lived perennial 

monocot herb with hollow stem up to 27-1/2 inches tall. The root 

system has a series of tuberlike parts at the base of the stem.

Leaves: Leaves are basal; the plant takes the form of a large 

tuft of onionlike rounded or slightly flattened hollow leaves, 4 to 12 

inches long; 3/16 inch in diameter; glabrous except on margins.

Flowers: Flowers February to May; the flowering inflorescence 

is a simple raceme or open panicle, 5-7/8 to 27-1/2 inches long, 

with widely spaced flowers; 3/16 to 1/2 inch wide with 6 tepals 

(petals and sepals) which are generally white or very pale pink with 

a neat central longitudinal stripe of brown to reddish-purple; flowers 

are diurnal, closing at night and in overcast or low light weather 

conditions.

Fruit: The fruit is a rounded capsule, 3/16 to 1/4 inch long, 

containing 6 seeds.

Habitat

Dry sandy or rocky disturbed sites such as waste places, pastures, 

and along roadsides and railroad rights-of-way within elevations that 

generally range below 4,600 feet.

Propagation/Phenology

Reproduces by seed. 

Comments

Native to Eurasia and North Africa; onionweed seeds prolifically 

and can establish large populations quickly and is drought resistant. 

Onionweed could be confused with some native onions (Allium L.); 

Federal (U.S.) noxious weed.
White Flowered Forbs

151

 Onionweed plant

© LR

Onionweed plant(s)

© USDA1

Onionweed flowers (below)

© LR

Onionweed flowering 

inflorescence

© ST
152

Oxeye Daisy

Leucanthemum vulgare Lam. (Aster family, Asteraceae)

Description

Prostrate, shallow-rooted, perennial forb with stems that sprout 

laterally from creeping root stock; when in flower, height ranges from 12 

to 36 inches tall and little branched. The root system is densely fibrous 

and forms offsets from short rhizomes.

Leaves: The central stem is glabrous to slightly hairy and often 

angular or furrowed; small tuft of basal leaves develops at the base of the 

plant, spatula-shaped, broadly toothed, and 2 to 5 inches long and 2 inches 

wide; while alternate leaves occur sparingly along the central stem, up 

to 5 inches long and 3/4 inch wide, becoming smaller as they ascend the 

stem, dark green on both sides, smooth, and glossy; lower leaves are often 

oblanceolate with slender petioles, while the middle to upper leaves are 

more oblong and often clasp the stem. Their margins are coarsely dentate, 

and some of the alternate leaves are often pinnatifid toward the base.

Flowers: Flowers May to August; 1 to 40, nearly naked stems end in 

a single daisy-like flower head, 1 to 2 inches across, with 15 to 35 white, 

oblong petalled ray flowers surrounding numerous tiny yellow, 5-lobed 

disk flowers; flower head receptacle noticeably flattened; at base of the 

flower head are several series of green floral bracts with membranous, 

brown margins that are brown and membranous.

Fruit: Fruit is a dark, oblong achene with 10 lighter colored ribs, less 

than 1/16 inch long; pappus lacking.

Habitat

Cultivated and disturbed or degraded sites on well-drained, but moist 

soils in meadows, grassland, woodland, and forest communities, and 

roadsides within elevations that generally range from 5,000 to 9,500 feet.

Propagation/Phenology

Reproduces both vegetatively and by seed; some estimates of total 

seed production per plant range from 1,300 to 4,000.

Comments

Native to Eurasia where it is allowed to grow undisturbed; oxeye 

daisy often forms dense colonies. This species generally occurs as a weed 

in wildland areas of the Southwestern Region rather than as an invasive 

plant.
White Flowered Forbs

153

Oxeye daisy flower 

heads (below)

© MEH

Oxeye daisy plants 

(above)

© MEH

Oxeye daisy upper 

stems and foliage (left)

© PTL

Oxeye daisy roots (above)

© SD
154

Poison Hemlock

Conium maculatum L. (Carrot family, Apiaceae)

Description

Poison hemlock is a much branched, warm-season, biennial forb 

5 to 8 feet tall; stems smooth, green to blue-green, hollow; stems 

usually spotted or streaked with red or purple on the lower half; 

large taproot, roots are long, forked, white to pale yellow and 1/2 to 

3/4 inch in diameter; when crushed, the leaves and root emit a rank, 

unpleasant odor sometimes compared to that of parsnips or celery; 

extremely poisonous. 

Leaves: Leaves are shiny green, finely pinnately divided 3 to 4 

times; leaflets are segmented and 1/8 to 1/4 inch long; lower leaves 

on long stalks stem-clasping; upper leaves on short stalks. 

Flowers: Flowers May to August; white flowers borne in many 

umbel-shaped clusters, each supported by a stalk; umbels 1-1/4 to 2 

inches broad; flowers lack sepals.

Fruit: Fruit is small, about 1/8 inch long; contains 2 concave, 

light brown, ribbed seeds; prominent wavy ribs and absence of oil 

cells between the ribs are important characters for distinguishing this 

fruit from others of the same natural order of plants. 

Habitat

Found on poorly drained soils, particularly near streams, ditches, 

and other surface water. It also appears on roadsides, edges of 

cultivated fields, and waste areas within elevations that generally 

range from 4,000 to 10,000 feet.

Propagation/Phenology

Reproduces by seed.

Comments

Native to the Mediterranean region; poisonous property occurs in 

all parts of the plant, including the large taproot. New Mexico Class 

B noxious weed.
White Flowered Forbs

155

Poison hemlock 

flowering umbel

© JDB

Poison 

hemlock 

spotted main 

stem

© JS

Poison 

hemlock 

plant

© JS

Poison 

hemlock 

fruit

© JS
156

White Clover

Trifolium repens L. (Pea family, Fabaceae)

Description

White clover is a cool-season perennial with a prostrate, 

stoloniferous growth form, 5 to 8 inches long. Leaves and roots 

develop along the stolon at the nodes. It also develops a taproot.

Leaves: The alternate leaves are composed of 3 leaflets 

(trifoliate), which may or may not have a “crescent” or “watermark” 

on the upper surface; membranous stipules lanceolate to ovate, 5/32 

to 13/16 inch long; leaf stalk long; leaflets obovate or oval, 3/16 to 

13/16 inch long, finely toothed; flowering stalks 2 to 12 inches long.

Flowers: Flowers June to September; the flower heads, each 

consisting of 40 to 100 flowers, are borne on long stalks from the leaf 

axils; flowers white but may have a pink hue; flower stalks 2 to 12 

inches long; flower heads spherical, 9/16 to 1 inch in diameter; flower 

stems less than 1/8 inch long, reflexed in age; flowers 3/16 to 3/8 inch 

long; calyx 1/8 to 3/16 inch long, tube white, teeth green; corolla 1/8 

to 3/8 inch long, white, sometimes with pink tinge.

Fruit: The fruit is a legume, less than 3/16 inch long, with 4 to 5 

seeds.

Habitat

White clover adapts only to soil with moderate to good moisture 

within elevations that generally range from 3,500 to 8,500 feet.

Propagation/Phenology

Reproduces by seed and by stoloniferous stems. White clover 

produces roughly 776,000 seeds per pound.

Comments

Native to Europe; white clover rapidly develops a deep fleshy 

taproot. Mature plants have roots 1 to 1-1/2 inches in diameter and 5 

to 8 feet deep. Many large and numerous smaller branches, all well 

supplied with laterals, spread rather widely and penetrate deeply, 

furnishing the plant with an excellent absorbing system. White clover 

may become weedy or invasive in some regions or habitats and 

may displace desirable vegetation if not properly managed making 

it a concern in riparian and moist meadow habitats. This species 
White Flowered Forbs

157

generally occurs as a weed in wildland areas of the Southwestern 

Region rather than as an invasive plant.

White clover 

flowers and 

foliage

© F&KS

White clover flowers (below)

© PJA

White clover plants (above)

© F&KS

White clover 

flowers, both fresh 

and mature (below)

© F&KS
158

White Sweetclover

Melilotus albus (L.) Lam. (Pea family, Fabaceae)

Description

Taprooted, erect, branched, annual, biennial, or short-lived 

perennial forb, 2 to 7 feet tall; larger plants branch frequently and 

are somewhat bushy in appearance, while shorter plants are less 

branched and rather lanky; stems are glabrous, furrowed, and 

angular; sometimes the lower stems are ribbed light red.

Leaves: The alternate compound leaves are trifoliate (cloverlike) 

and hairless; each leaflet is about 3/4 inch long, and 1/4 inch wide, 

oblong, oblanceolate, or obovate in shape, and dentate along the 

middle or upper margin; terminal leaflet has a short stalk at its base, 

while the lateral leaflets are nearly sessile; petiole of each compound 

leaf is about 1/2 inch long; there are a pair of small linear stipules at 

its base.

Flowers: Flowers April to September; spikelike racemes of 

white flowers are abundantly produced; each raceme is up to 6 

inches long and has dozens of yellow to cream-colored flowers; 

flowers about 5/16 inch long; when fully open, it has a pealike floral 

structure with an upper standard and lower keel.

Fruit: Fruit is a small seedpod, less than 3/16 inch long, 

conspicuously cross-ribbed and contains 1 to 2 seeds; seeds are 

tannish-yellow and somewhat flattened and kidney shaped.

Habitat

Cultivated and disturbed or degraded sites in meadows, 

grassland, woodland, and forest communities, and roadsides within 

elevations that generally range from 5,000 to 10,500 feet.

Propagation/Phenology

Reproduces by seed; well-developed plants may produce more 

than 1,000 seeds.

Comments

Native to Eurasia; white sweetclover is very similar to M. 

officinal (yellow sweetclover), which is another weedy species 

native to Eurasia; yellow sweetclover stems are glabrous, furrowed, 
White Flowered Forbs

159

White sweetclover 

flower inflorescences

© JN

and angular; sometimes the lower stems are ribbed light 

red, and its slightly reticulated seedpods lack conspicuous 

cross ribs; otherwise, these two species are nearly identical; 

USDA Plants Database considers them synonymous. White 

sweetclover generally occurs as a weed in wildland areas of the 

Southwestern Region rather than as an invasive plant.

White sweetclover flowers

© EB

White sweetclover trifoliate leaf

© G&AD

White sweetclover 

plant(s)

© G&AD
160

Whitetop

Cardaria draba (L.) Desv. (Mustard family, Brassicaceae)

Description

Multi-stemmed perennial forb, 18 to 20 inches tall; erect stems 

sparse to densely covered with simple short hairs; seed production 

is prolific; new shoots arise from buds on lateral roots or root 

fragments; establishes dense stands that exclude other vegetation.

Leaves: Gray-green, alternate, obovate, lanceolate, and oblong 

to elliptic; surfaces, especially lower, sparsely to densely covered 

with simple, short white hairs, margins irregularly toothed to entire; 

basal leaves short-stalked 3-1/2 inches long and 1-1/2 inches wide; 

sessile upper leaves are sparsely to densely hairy with rounded to 

acute-lobed bases that clasp the stem.

Flowers: Flowers March to July; inflorescences often flattopped; small (3/16 inch long), fragrant, white 4-petaled, flowers are 

numerous; sepals are glabrous.

Fruits: Pods upside-down, heart-shaped to broadly ovate 

in outline, 1/8 to 3/16 inch long, 1/8 to 1/4 inch wide, glabrous; 

style persistent, 1/16 to 1/8 inch long at the apex; seeds 1 to 2 per 

chamber, ovoid, slightly flattened, reddish-brown, less than 1/8 inch 

long and 1/16 inch wide.

Habitat

Cultivated and disturbed or degraded moist sites in meadows, 

grassland, chaparral, woodland, forest, and riparian communities, 

and roadsides; generally grows on alkaline to saline soils, but 

tolerates many soil types and moisture conditions within elevations 

that generally range from 3,000 to 8,000 feet.

Propagation/Phenology

Reproduces vegetatively from creeping roots and less 

importantly by seed. Seedlings develop tap roots to a depth of 10 

inches or more and lateral roots with shoot buds within 1 month. 

This species is an aggressive weed; mature plants develop extensive 

systems of persistent, deep vertical and horizontal roots to depths 

of 6-1/2 feet or more. Root fragments generate new plants, but 

regeneration is poor in dry soils.
White Flowered Forbs

161

Comments

Native to central Asia; this species is difficult to 

distinguish from lens-podded hoarycress and hairy whitetop in 

the seedling and vegetative states. Arizona prohibited/restricted 

noxious weed and New Mexico Class A noxious weed.

Whitetop plant

© BR

Whitetop plants

© CE

Whitetop fruit

© JMD

Whitetop flowers

© BR
162
Yellow Flowered Forbs

163

Tansy ragwort © MS
164

Black Medick

Medicago lupulina L. (Pea family, Fabaceae)

Description

Shallow, taprooted, low, trailing winter annual or short-lived perennial 

forb, with prostrate or ascending stems up to 30 inches long; where thick 

stands develop, stems may become erect, obtaining heights of 18 to 24 

inches; 4-angled stems are typically purple at the base, hairless or more 

rarely with some short hairs, although older stems become less hairy; they 

branch occasionally.

Leaves: Alternate, compound leaves are trifoliate (cloverlike); 

younger leaves, toward the stems tips, have short hairy petioles; older 

leaves have longer petioles (up to 1-3/16 inches long); paired stipules at 

petiole base are lanceolate to ovate and variable in size; leaflets are up 

to 9/16 inch long and about half as wide; medium to dark green, wedge 

shaped or obovate, hairy or nearly hairless, finely toothed with prominent 

veins. 

Flowers: Flowers February to December; 2 to 8 small, bright yellow 

flowers are borne in clusters about 1/2 to 3/4 inch long; each flower is 

about 1/8 inch long; when fully open, it has a pealike floral structure with 

an upper standard and lower keel.

Fruit: Fruit is a spirally twisted, thick-walled pod; each pod is black, 

about 1/8 inch long and contains a single dark seed that is somewhat 

flattened and kidney shaped, less than 1/8 inch long.

Habitat

Cultivated and disturbed or degraded sites in meadows, grassland, 

woodland, and forest communities, and roadsides within elevations that 

generally range from 4,000 to 8,000 feet.

Propagation/Phenology

Reproduces by seed; one well-developed, vigorous, plant may produce 

more than 1,000 seeds.

Comments

Native to Eurasia and Africa; black medick easily spreads and can 

form large colonies and where it is allowed to grow undisturbed, black 

medick may displace native species. Prior to fruiting, black medic could 

be confused with burclover. This species generally occurs as a weed in 

wildland areas of the Southwestern Region rather than as an invasive plant.
Yellow Flowered Forbs

165

Black medick flowers 

and foliage

© KAR

Black medick 

trifoliate leaf

© PJA

Black medick plant(s)

© F&KS

Black medick flowers

© RHM
166

Black Mustard

Brassica nigra (L.) W.D.J. Koch (Mustard family, Brassicaceae)

Description

Erect annual, taprooted forb, 2 to 8 feet tall; stems usually glabrous 

and glaucous, sometimes with scattered stiff hairs toward the base; upper 

stems terminate in narrow racemes of yellow flowers.

Leaves: The alternate leaves are 2 to 10 inches long, 1 to 6 inches 

wide, becoming smaller as they ascend the stems; lower leaves are 

pinnately lobed and obovate in outline, tapering to a long and rather 

stout petiole (not clasping), terminal lobe much larger than the lateral 

lobes, upper surface, often bristly with scattered hairs that are stiff, short, 

and white, lower surface usually glabrous, except for a few hairs along 

the central vein; upper leaves often lanceolate, broadly elliptic, or some 

other odd shape, 1 to 2 lobed or none. 

Flowers: Flowers May to July; narrow racemes of yellow flowers, 

6 to 24 inches long when fully mature; flower up to 5/16 inch across, 

consisting of 4 sepals and 4 yellow petals. The sepals are initially green, 

but become yellow while the flower blooms. The petals are well rounded 

toward their tips.

Fruit: Fruit is a silique, 5/8 inch long, tapering to a conical beak, 

appressed against the stalk of the raceme as it matures; petiole of silique 

(or flower) is about 5/16 inch long; seeds are dark brown or black.

Habitat

Black mustard occurs in dry disturbed sites such as waste places, 

pastures, and along roadsides and railroad rights-of-way within 

elevations that generally range below 7,000 feet.

Propagation/Phenology

Reproduces by seed.

Comments

Native to Eurasia; black mustard seeds and foliage have a pungent 

taste. Black mustard grows profusely and produces allelopathic 

chemicals that prevent germination of native plants; in addition, the 

seeds contain an alkaloid and the sinapina the glucoside sinigrin. This 

species generally occurs as a weed in wildland areas of the Southwestern 

Region rather than as an invasive plant.
Yellow Flowered Forbs

167

Black mustard flowers

© F&KS

Black mustard fruit

© JMD

Black mustard plants (below)

© F&KS

Black mustard plant(s)

© F&KS
168

Burclover

Medicago polymorpha L. (Pea family, Fabaceae)

Description

Shallow, taprooted, low, trailing annual or short-lived perennial 

forb, with prostrate or ascending stems up to 30 inches long; where 

thick stands develop stems may become erect, obtaining heights of 18 

to 24 inches; 4-angled stems are light green or reddish green, hairless 

or more rarely with some short hairs, although older stems become less 

hairy; they branch occasionally.

Leaves: Alternate, compound leaves are trifoliate (clover-like); 

younger leaves, toward the stems tips, have short hairy petioles; 

older leaves have longer petioles; paired stipules at petiole base are 

lanceolate to ovate and variable in size; leaflets are up to 9/16 inch 

long and about half as wide; medium to dark green, wedge-shaped or 

obovate, hairy or nearly hairless, finely toothed with prominent veins. 

Flowers: Flowers April to September; 2 to 8 small, bright yellow 

flowers are borne in clusters about 1/2 to 3/4 inch long; each flower is 

about 1/8 inch long; when fully open, it has a pealike floral structure 

with an upper standard and lower keel.

Fruit: Fruit is a spirally twisted, hooked-spined, thick-walled pod; 

each pod is dark colored, about 1/8 inch long and contains a single 

dark seed that is somewhat flattened and kidney shaped, less than 1/8 

inch long.

Habitat

Cultivated and disturbed or degraded sites in meadows, grasslands, 

woodlands, and forest communities, and roadsides within elevations 

that generally range from 4,000 to 8,000 feet.

Propagation/Phenology

Reproduces by seed; well-developed plants may produce more 

than 1,000 seeds.

Comments

Native to southern Europe; where it is allowed to grow 

undisturbed, burclover may displace native species. Prior to fruiting, 

burclover could be confused with black medic. Arizona prohibited/

regulated noxious weed.
Yellow Flowered Forbs

169

Burclover 

flowers and 

foliage

© SM

Burclover 

flowers

© SM

Burclover flower, 

stem, foliage, and 

fruit

© AD

Burclover fruit

© SM
170

Curveseed Butterwort

Ceratocephala testiculata (Crantz) Roth

(Buttercup family, Ranunculaceae)

Description

Decumbent to erect, cool-season annual, rarely branching at the 

base, usually less than 4 inches tall; covered with woolly hairs.

Leaves: Grayish-green leaves are attached at the base on petioles 

less than 1-3/16 inches long, leaf blades broadly spatulate in outline, 

3/16 to 1-3/16 inches long; however, blades are divided into 2 to 3 

linear segments.

Flowers: Flowers April to June; solitary yellow flowers on 

peduncles as long as or shorter than leaves; receptacle covered with 

densely matted hair; 5 green sepals 3/32 to 5/16 inch long, spreading, 

persistent in fruit, also covered with densely matted hair; 5 yellow 

petals 3/32 to 5/16 inch long, 3/16 inch wide or less, nonpersistent.

Fruit: Fruit is an achene; achene clusters ovoid to spheric in 

shape, 3/8 to 1-1/16 inch long, 5/16 to 3/8 inch wide; achenes plump, 

1/16 to 3/32 inch long, less than 3/32 inch wide, finely covered with 

matted hair or glabrous; spinelike persistent beak 1/8 to 3/16 inch long, 

straight; when dry the seed pods are very prickly.

Habitat

Curveseed butterwort occurs in dry disturbed sites such as waste 

places, meadows and pastures, and along roadsides especially in 

semidesert and Great Basin grasslands, and in woodland and shrubland 

communities within elevations that generally range from 1,300 to 

9,000 feet.

Propagation/Phenology

Reproduces by seed.

Comments

Native to Eurasia; curveseed butterwort often occurs in dense mats 

which cover large areas of the ground making it highly competitive. 

Curveseed butterwort contains ranunculin, which changes into a highly 

toxic compound, protoanemonin, when the plant is crushed; it is highly 

toxic to sheep. This species generally occurs as a weed in wildland 

areas of the Southwestern Region rather than as an invasive plant.
Yellow Flowered Forbs

171

Curveseed 

butterwort flower

© GAM

Curveseed 

butterwort plant

© GAM

Curveseed 

butterwort fruit

© DWT

Curveseed 

butterwort 

fruit

© BM
172

Dalmatian Toadflax

Linaria dalmatica (L.) Mill. ssp. dalmatica

(Figwort family, Scrophulariaceae)

Description

Erect, single or multi-stemmed, clump or patch-forming perennial 

forb; 16 to 36 inches tall; with creeping roots and showy yellow 

flowers; flowers are borne in axils of an elongated dense or open 

raceme, with an erect or drooping tip. 

Leaves: Leaves primarily alternate, but crowded and often 

appearing opposite or whorled, especially near the bases of stems; 

margins entire, sessile, linear; 7/8 to 1-5/8 inches long and 1/2 to 3/4 

inch wide; palmately veined with an acute apex; upper leaves are 

conspicuously broad-based and clasping the stem.

Flowers: Flowers May to September. Flowers showy, bright 

yellow (sometimes white), snapdragon-like, 2-lipped, 5-lobed, with 

a long, straight, downward pointing spur near the base of the lower 

corolla tube; 1-3/8 to 2-1/8 inches long, including spur; throat and 

lower lip white- or orange-hairy; flowers in bud often purplish at apex.

Fruit: Round, 2-chambered capsule, 1/8 to 3/8 inch long; opening 

by irregular slits at the apex to release numerous black to brown, 1/16 

inch long, ridged, pyramidlike seeds.

Habitat

Cultivated and disturbed or degraded sites in meadows, grassland, 

woodland, and riparian communities, and roadsides within elevations 

that generally range from 4,400 to 10,000 feet.

Propagation/Phenology

Reproduces by seed (up to 500,000) and vegetatively from 

creeping lateral roots; plants develop an extensive system of vertical 

and lateral roots that produce new shoots; root fragments can 

produce new plants; plants can rapidly colonize a site by vegetative 

reproduction from creeping roots. 

Comments

Native to southeast Europe; an extensive root system makes this 

plant difficult to control; Dalmatian toadflax and yellow toadflax 

can hybridize. Arizona prohibited/restricted noxious weed and New 

Mexico Class A noxious weed.
Yellow Flowered Forbs

173

Dalmatian toadflax 

flowers (above)

© LW

Dalmatian toadflax flowers 

(below)

© USU

Dalmatian toadflax 

foliage

© BM

Dalmatian 

toadflax plants 

(right)

© BM
174

Dyer’s Woad

Isatis tinctoria L. (Mustard family, Brassicaceae)

Description

Erect, multi-stemmed biennial, sometimes winter annual or 

short-lived perennial forb, 12 to 48 inches tall; immature taprooted 

plants exist as basal rosettes until flowering stems develop at 

maturity.

Leaves: Leaves are opposite, simple, petiolate, bluish-green, 

often covered with a powdery white bloom; midnerve conspicuously 

pale; rosette leaves oblanceolate to elliptic, 1-1/4 to 7 inches long 

and 1/2 to 1-5/8 inches wide, tips rounded, bases gradually tapered 

to stalk, 1/2 to 3/4 the length of the blade; margins weakly toothed 

to wavy. Stem leaves alternate, sessile, and broad to narrowly 

arrowhead-shaped with smooth margins, sometimes broadest near 

the tip; with short basal lobes clasping the stem.

Flowers: Flowers April to June; yellow 4-petaled, 1/4 inch wide 

flowers in flat-topped or umbrella-shaped clusters.

Fruit: Fruits are flat, teardrop shaped, 3/8 to 3/4 inch long and 

1/4 to 5/16 inch wide, black to blue- or purplish-black at maturity, 

pendulous, and each contains a single seed.

Habitat

Cultivated and disturbed or degraded sites in grassland and 

woodland communities, and roadsides; often growing on dry, rocky, 

or sandy soils within elevations that generally range from 4,300 to 

7,000 feet.

Propagation/Phenology

Reproduces by seed; most seed falls near the parent plants; seeds 

mature about 8 weeks after flower stem initiation.

Comments

Native to Europe; plants cut above the root crown can grow new 

shoots and may persist as short-lived perennials. Arizona prohibited 

noxious weed and New Mexico Class A noxious weed.
Yellow Flowered Forbs

175

Dyer’s woad flowers, immature 

(middle) and mature (bottom) fruit

© SD

Dyer’s woad flowers

© SD

Dyer’s woad plants

© JMD

Dyer’s woad 

plants

© SD
176

Floating Primrose-Willow

Ludwigia peploides (Kunth) P.H. Raven ssp. montevidensis

(Spreng.) P.H. Raven (Evening Primrose family, Onagraceae)

Description

Floating primrose-willow is a prostrate, glabrous to sticky 

villous, aquatic, perennial forb, rooting at the nodes, 20 to 120 inches 

long to 32 inches tall.

Leaves: Leaves are alternate, more or less clustered, 1/8 to 4 

inches long, dark shiny green, net-veined (lateral veins 7 to 11 per 

side); leaf base narrowly wedge shaped; leaf apex acute to acuminate 

or obtuse, tip glandular; early growth consists of rosette-like clusters 

of rounded leaves on water surface; at flowering leaves lengthen to 

lanceolate or elliptic shape; petiole 3/16 to 1-3/8 inches long.

Flowers: Flowers May to October; yellow flowers solitary; 

five green sepals hairy, less than 1/16 inch long; five yellow petals; 

anthers in two whorls; ovary truncate at apex, dense pubescent with 

dry, short white hairs, sometimes restricted to the apex of the ovary; 

style yellow, densely long-hairy in lower half or higher; stigma 

lemon yellow.

Fruit: Fruit is a capsule 3/8 to 1-1/2 inches long, 1/16 to 3/16 

inch in diameter, woody with thick walls, sometimes almost glabrous 

or sparsely or densely villous with short hairs often somewhat 

curved, somewhat five angled, scarcely narrowed at apex, abruptly 

narrowed at base, irregularly and tardily opening; seeds rectangular, 

wrinkled, dull brown less than 1/16 inch long.

Habitat

Wet sites such as ponds and creeks within elevations that 

generally range below 6,400 feet.

Propagation/Phenology

Reproduces vegetatively by stem fragmentation and by seed.

Comments

Native to South America; floating primrose-willow has two types 

of roots: one type absorbs nutrients and attaches the plant to the soil, 

and the other type is adventitious, located along the stems which 
Yellow Flowered Forbs

177

ensure oxygen uptake and favor rooting of plant fragments. 

Floating primrose-willow occasionally forms masses that can 

obstruct navigation. This species generally occurs as a weed 

in wildland areas of the Southwestern Region rather than as an 

invasive plant.

Floating primrose-willow 

flower and foliage

© BB

Floating primrose-willow 

flower and foliage

© BB

Floating primrosewillow plant(s)

© GL

Floating primrose-willow 

infestation

© GL
178

Globe Chamomile

Oncosiphon piluliferum (L.f.) Källersjö 

(Aster family, Asteraceae)

Description

Annual, taprooted forb, 12 to 24 inches tall; herbage has a very 

displeasing odor.

Leaves: Opposite, deeply lobed, 3/4 to 1-3/8 inches long, 

ultimate lobes linear to spatulate or oblanceolate, less than 1/16 inch 

wide, sparsely puberulent or set with stiff, slender bristles, minutely 

gland-dotted (in pits). 

Flowers: Flowers March to May; yellow inflorescence is 

globelike, approximately 1/8 to 1/2 inch in diameter; flower heads 

borne singly or two to four in corymbiform arrays; peduncles 3/8 to 

3-1/8 inches long; pappus is a very small crown of white scales to 

1/32 inch long.

Fruit: Fruit is an achene, less than 1/16 inch long, less than 1/32 

inch wide, curved, ribbed on the inner face.

Habitat

Globe chamomile occurs in dry disturbed sites such as waste 

places, pastures, and along roadsides within elevations that generally 

range below 3,500 feet.

Propagation/Phenology

Reproduces by seed. It is a prolific seeder and appears to 

germinate in all but the summer months.

Comments

Native to South Africa; foliage has a pungent odor. Globe 

chamomile shows weedy tendencies by invading especially disturbed 

areas and cultivated fields. Being an annual, globe chamomile is 

clearly a pioneer species of disturbed sites. This species generally 

occurs as a weed in wildland areas of the Southwestern Region rather 

than as an invasive plant.
Yellow Flowered Forbs

179

Globe chamomile flower head

© RS

Globe chamomile plant(s)

© G&AD

Globe chamomile 

foliage

© X

Globe chamomile 

flower heads

© LM
180

Leafy Spurge

Euphorbia esula L. (Spurge family, Euphorbiaceae)

Description

Erect, clump or patch-forming perennial with milky white latex 

juice, 12 to 36 inches tall; plants develop extensive creeping root 

systems and are highly variable; stems are more or less woody at the 

base; stems erect, glabrous or hairy.

Leaves: Leaves sessile, glabrous, mostly alternate (some may be 

opposite or whorled just below the inflorescence branches); leaves 

linear to narrowly oblanceolate, 7/8 to 4 inches long and typically 

about 1/4 inch wide, with acute or rounded tips, margins smooth; 

yellow-green inflorescence bracts opposite, heart to kidney-shaped, 

sessile, glabrous, shorter and broader than leaves; stipules absent.

Flowers: Flowers June to September; flowers are yellowishgreen, small, arranged in small clusters and subtended by paired 

heart- or kidney-shaped yellowish-green bracts.

Fruit: Round, 3-chambered capsules, 1/8 to 1/4 inch long, 

smooth to granular with 1 yellow-brown to gray or mottled, smooth 

seed per chamber. Seeds ovoid to oblong, round in cross-section, 

1/16 to 1/8 inch long.

Habitat

Cultivated and disturbed or degraded sites in fields, pastures, 

rangeland and riparian communities, and roadsides within elevations 

that generally range from 4,600 to 9,500 feet. 

Propagation/Phenology

Reproduces by seed and vegetatively from extensively creeping 

roots; develops an extensive system of vigorous, spreading, rhizomelike long horizontal roots, short horizontal feeder roots, and short and 

long vertical roots; long horizontal roots and crowns produce many 

pink scaly buds from which new shoots can develop; most root buds 

develop within 1 foot of the soil surface, but a few can develop as 

deep as 10 feet.

Comments

Native to southwestern Europe; mature capsules rupture and 

forcefully eject seeds up to 16 feet from the parent plant; infestations 
Yellow Flowered Forbs

181

Leafy spurge flowers

© USDA1

Leafy spurge stem 

and foliage (right)

© SD

Leafy spurge plant

© JMR

Leafy spurge rhizomes with 

characteristic pink nodes (above)

© SD

are usually initiated by seed, but population expansion is 

mostly vegetative. Arizona prohibited noxious weed and New 

Mexico Class A noxious weed.
182

Little Hogweed 

Portulaca oleracea L. (Purslane family, Portulacaceae)

Description

Annual plant forms a spreading mat up to 6 inches tall and 2 feet 

across, branching frequently at the base in a radiating pattern from a 

taproot; stems are round, thick, and succulent; stems range in color 

from light green to reddish brown. 

Leaves: The leaves are rather thick and succulent; shiny green; 

somewhat teardrop-shaped, up to 1 inch long and 1/2 inch wide, are 

alternate or nearly opposite and sessile along the stems.

Flowers: Flowers April to September; five yellow petalled 

flowers occur singly or in small terminal clusters, flowers about 1/4 

inch across, consisting of floppy petals that open up for a few hours 

during bright sunny mornings.

Fruit: Each flower is replaced by a seed capsule that splits open 

around the middle to release the numerous small seeds; seeds dark 

brown or black, somewhat flattened, and nearly round or kidneyshaped; surface is granular, appearing somewhat coiled.

Habitat

Cultivated and disturbed or degraded sites in meadows, 

grassland, woodland, and forest communities, and roadsides in 

practically any kind of soil containing loam, sand, or gravelly 

material within elevations that generally range from 4,000 to 8,500 

feet.

Propagation/Phenology

Reproduces by seed or vegetatively, as the broken-off stems can 

form rootlets to establish new plants.

Comments

Native to Europe; the fleshy stems and leaves provide this 

plant with a distinctive appearance; tolerance to heat and drought is 

excellent. This species generally occurs as a weed in wildland areas 

of the Southwestern Region rather than as an invasive plant. Arizona 

prohibited/regulated noxious weed.
Yellow Flowered Forbs

183

Little 

hogweed 

flowers, 

stems, and 

foliage

© PW2

Little hogweed 

seedlings 

(above)

© USU

Little 

hogweed 

plants

© F&KS

Little hogweed 

flowers and foliage 

(left)

© USU
184

Malta Starthistle

Centaurea melitensis L. (Aster family, Asteraceae)

Description

Erect multi-branched annual or biennial forb to 39 inches tall, with 

spiny or comb-like flower head bracts; taprooted plants exist as basal 

rosettes until erect, highly branched flowering stems are produced in 

late spring/summer.

Leaves: Stem leaves alternate, mostly linear or narrowly oblong 

to oblanceolate, margins smooth or wavy; leaf bases extend down the 

stems and give stems a winged appearance; wings to 3/16 inch wide; 

foliage grayish-green; leaves evenly covered with thick stiff hairs and 

minute resinous dots, and sparsely covered with fine white cottony 

hairs that do not hide the stiff hairs and resinous dots; new leaves are 

often densely covered with fine cottony hairs.

Flowers: Flowers April to December; heads ovoid, spiny, solitary 

on stem tips, consist of numerous yellow 7/16 to 9/16 inch flowers; 

flower head bracts palmately spined, with one long central spine and 

three to four pairs of short lateral spines; sparsely covered with cottony 

hairs or with patches at the spine bases; central spine 1/4 to 5/8 inch 

long, slender, purple to brown tinged.

Fruit: Achenes barrel-shaped, compressed, laterally notched at 

the base, 1/16 to 1/8 inch long, finely pubescent, grayish to tan with 

slightly darker stripes, bases deeply notched, narrow, hook-like; 

pappus bristles pale tan, slender, stiff, unequal, less than 1/8 inch long.

Habitat

Cultivated and disturbed or degraded sites in grassland and 

woodland communities, and roadsides within elevations that generally 

range below 7,200 feet.

Propagation/Phenology

Reproduces by seed, production is highly variable, can produce 1 

to 60 or more seeds per head and 1 to 100 heads or more per plant. 

Comments

Native to southern Europe; Malta starthistle is a very competitive 

and aggressive plant with allelopathic effects; stands of Malta 

starthistle may persist indefinitely once established; looks very similar 

to yellow starthistle. New Mexico Class B noxious weed.
Yellow Flowered Forbs

185

Malta starthistle 

flower heads (left)

© JMR

Malta starthistle 

flower head (right)

© JMR

Malta 

starthistle 

flower heads 

and foliage

© JMD

Malta starthistle 

basal rosette

© JMD
186

Mediterranean Sage

Salvia aethiopis L. (Mint family, Lamiaceae)

Description

Erect, coarse, herbaceous, warm-season, biennial or short-lived 

perennial forb with square stems and stout taproot, up to 3 feet 

tall; fine, woolly hairs cover the stems; aromatic (sage-like) when 

crushed.

Leaves: Rosette leaves petiolate and 4 to 12 inches long, ovate, 

coarsely toothed on the margins; densely covered with woolly 

grayish-white hairs; rosettes can be 1 to 4 feet in diameter; stem 

leaves are opposite, becoming smaller toward the stem tip.

Flowers: Flowers July to August; flowering stems are highly 

branched, with whorls of 5 to 10 flowers; flowers pale yellow to 

whitish and strongly 2-lipped, 5/8 to 3/4 inch long; sepals about 3/8 

inch long; lobes spine-tipped, and covered with fine white woolly 

hairs.

Fruit: Fruit is an egg-shaped, smooth, brown nutlet, about 3/16 

inch long; four nutlets per flower, enclosed by the persistent sepals; 

each nutlet produces four brown seeds about 1/8 inch long, with dark 

nerves.

Habitat

Cultivated and disturbed or degraded well drained sites in 

meadows, grassland, woodland, and riparian communities, and 

roadsides within elevations that generally range below 8,500 feet.

Propagation/Phenology

Reproduces by seed; single plant can produce 50 to 100,000 

seeds; flowering stems typically break off at a point below the 

panicle and disperse seed by tumbling with the wind.

Comments

Native to Europe; mature Mediterranean sage plants do not 

resemble any native sages and are unlikely to be confused with 

them, however, rosettes of Mediterranean sage may be confused with 

wooly mullein rosettes. This species generally occurs as a weed in 

wildland areas of the Southwestern Region rather than as an invasive 

plant.
Yellow Flowered Forbs

187

Mediterranean sage flowers 

© EL

Mediterranean sage in bloom

© LLB

Mediterranean sage 

rosette

© LA

Mediterranean sage 

infestation (below)

© EC
188

Perennial Sowthistle

Sonchus arvensis L. (Aster family, Asteraceae)

Description

Vigrous herbaceous perennial, with hollow stems, milky sap and 

creeping roots that produce new shoots, 2 to 3-1/2 feet tall, branching 

occasionally in the upper half; the bluish-green stems; lower stems 

leafy, upper stems can be glabrous or glandular-hairy; plants are 

highly competitive, persistent, and can rapidly colonize new sites by 

vegetative reproduction.

Leaves: Leaves alternate, highly variable, entire to deeply pinnatelobed, 3/4 to 12 inches long, 3/4 to 4 inches wide, clasping the stem 

at the base with rounded basal lobes; lobes triangular, often curved 

backwards, usually 2 to 7 per side; terminal lobe typically longer, 

broader than lateral lobes; margins with small, spiny teeth; upper 

leaves sessile, often unlobed, lower leaves short-petioled, lobed.

Flowers: Flowers June to October; flower heads 1-3/16 to 2 inches 

wide, consisting of numerous bright yellow to orange-yellow 5-lobed 

ray flowers at the stem tips. Pappus bristles fine, soft, white, numerous, 

5/16 to 7/16 inch long; flower head stalks and flower head bracts 

typically covered with stiff glandular hairs; bracts about 3/4 inch long; 

flower heads open about 2 to 3 hours after sunrise and close near noon.

Fruit: Fruit is an oblong, flattened, 3 to 4 angled achene, with two 

minutely wrinkled longitudinal ridges between angles, less than 1/8 

inch long and less than 1/16 inch wide, light to dark brown.

Habitat

Cultivated and disturbed or degraded moist sites in grassland, 

woodland, and riparian communities, and roadsides in any type of 

non-compacted, fine, rich, and slightly alkaline to neutral soils within 

elevations that generally range from 5,000 to 6,000 feet.

Propagation/Phenology

Reproduces by seed and vegetatively; stoutly taprooted to depths 

of 9 feet, it also produces long spreading rhizomes.

Comments

Native to Europe; an extensive root system makes field sowthistle 

difficult to control. Arizona prohibited noxious weed.
Yellow Flowered Forbs

189

Pedrennial sowthistle mature and 

immature flower heads

© TH

Perennial sowthistle fruit

© DC

Perennial sowthistle plants

© SD

Perennial sowthistle leaf base and 

stem

© MS
190

Perennial Wallrocket 

Diplotaxis tenuifolia (L.) DC. (Mustard family, Brassicaceae)

Description

Erect, perennial subshrub or forb that forms a dense, bushy 

rosette with erect branched stems usually 12 to 48 inches tall, large 

taproot; foliage is aromatic when crushed.

Leaves: Basal rosette leaves are succulent, bluish to dark green, 

lance shaped, up to 2-3/4 to 5-7/8 inches long and 1-1/4 inches wide 

with irregular lobes, slightly pubescent; mainly confined to the lower 

parts of the stems and rosette; lower leaves are long-stalked, entire, 

coarsely lobed, or toothed; upper stem leaves are small, stalkless, 

unlobed, and almost bract-like.

Flowers: Flowers May to October; bright yellow flowers, 9/16 to 

11/16 inch across; on long peduncles two to three times the length of 

the flowers; four rounded petals each about 5/16 to 3/8 inch long.

Fruits: Pod (silique) straight, flat, 3/8 to 2 inches long by 3/16 

inch in diameter with a small beak-shaped end; seeds arranged in two 

rows; up to 60 seeds per fruit.

Habitat

Cultivated areas and disturbed or degraded sites in meadows, 

grassland and riparian communities, and roadsides; preferring 

shallow, porous calcareous soils within elevations that generally 

range below 4,000 feet.

Propagation/Phenology

Reproduces by seed.

Comments

Native to Eurasia; edible, branches often used as an ingredient 

for salads. New Mexico Watch List species.
Yellow Flowered Forbs

191

Perennial wallrocket flowers

© LR

Perennial 

wallrocket 

plants

© LR

Perennial wallrocket foliage

© LR

Perennial 

wallrocket 

flower and 

fruit (above)

© LR
192

Puncturevine 

Tribulus terrestris L. (Creosote-bush family, Zygophyllaceae)

Description

Annual plant develops a mat of prostrate stems that range from 

1 to 3 feet across; branches frequently at the base and occasionally 

elsewhere; round stems are initially green, but quickly become brown; 

they are densely covered with short hairs and sparsely covered with 

long hairs; root system consists of a stout taproot that can extend 

several feet into the ground.

Leaves: Compound leaves are evenly pinnate, 2 to 4 inches long, 

consisting of four to eight pairs of leaflets, with a hairy central stalk; 

dark, short petioled, green leaflets are up to 3/4 inch long and 1/4 inch 

wide, oblong, smooth along the margins, and sparsely to moderately 

hairy.

Flowers: Flowers April to October; flowers occur individually 

from the axils of the compound leaves on hairy pedicels about 1/2 to 

3/4 inch long; each bright yellow 5-petalled flower is about 1/2 inch 

across, with five triangular green sepals; the petals are well rounded 

and longer than the sepals.

Fruit: Fruit is a stout-spined bur that divides into five wedgeshaped segments, gray to yellowish-tan, hairy, to 3/8 inch in diameter, 

flattened, lobed, with two stout spines 1/8 to 1/4 inch long and several 

prickles; seeds usually three to five per segment, remain enclosed 

within burs.

Habitat

Cultivated and disturbed or degraded moist sites in grassland, 

woodland, and riparian communities, and roadsides growing best on 

dry, sandy soils, but tolerates most soil types within elevations that 

generally range below 7,000 feet.

Propagation/Phenology

Reproduces by seed; plants typically bear numerous burs (average 

200 to 5,000) and often forms colonies at favorable sites. 

Comments

Native to the Mediterranean region; puncturevine is unlikely to 

be confused with other weeds. Arizona prohibited/regulated noxious 

weed.
Yellow Flowered Forbs

193

Puncturevine 

flower and 

foliage

© F&KS

Puncturevine 

flower, foliage, 

and immature 

fruit (right)

© USU

Puncturevine plants (below)

Puncturevine mature fruit 

(left)

© USU
194

Rush Skeletonweed

Chondrilla juncea L. (Aster family, Asteraceae)

Description

Erect, multi-stemmed perennial (sometimes) biennial forb to 39 

inches tall, with rigid, wiry flowering stems, milky sap; plants exist 

as basal rosettes until flowering stems develop at maturity and rosette 

leaves whither; taproot slender, deep, persistent, with short lateral 

branches along the length.

Leaves: Rosette leaves oblanceolate, 3/16 to 7/16 inch long 

and 3/8 to 2 inches wide, prostrate, typically lacking hairs; margins 

often purple-tinged and irregularly shallow-lobed, with lobes often 

pointing backward toward the leaf base, terminal lobe more or less 

sharp-pointed; upper stems mostly lack hairs, but typically have 

dense, bristly, downward pointing hairs at the base; stem leaves 

often absent or bract-like, but when present resemble reduced rosette 

leaves.

Flowers: Flowers July to November; flower heads axillary or 

terminal, sessile or short-stalked, and solitary or in interrupted spikelike clusters of 2 to 5; flower head consists of 7 to 12 bright yellow 

flowers 9/16 to 3/4 inch long (strap-shaped with 5-lobed corollas); 

flower head bracts cylindrical and in two unequal rows, the outer 

much smaller than the inner.

Fruit: Achene body oblong tapered at both ends, hairless, pale 

to dark brown, 3/16 inch long, with many lengthwise ribs, up to six 

small scales at the apex, surrounding the point of beak attachment; 

beak slender, 1/4 inch long, not including the pappus which consists 

of many equal, fine, white bristles about 1/4 inch long.

Habitat

Cultivated and disturbed or degraded sites in grassland and 

woodland communities, and roadsides on well-drained, sandy or 

gravelly soils within elevations that generally range below 5,500 

feet.

Propagation/Phenology

Reproduces only by clones produced vegetatively from 

adventitious buds on roots and asexually by apomictic (without 

fertilization) seed; a single plant can produce 15,000 to 20,000 seeds 

per season.
Yellow Flowered Forbs

195

Rush skeletonweed 

flower heads

© RO

Rush skeletonweed flowering stem

© SD

Rush skeletonweed basal foliage similar to 

dandelion and chicory

© JMD

Rush skeletonweed 

plants

© USU

Comments

Native to southern Europe; tolerates a wide variety of 

environmental conditions; immature plants look similar to 

dandelion and chicory. Arizona prohibited noxious weed.
196

Saharan Mustard

Brassica tournefortii Gouan (Mustard family, Brassicaceae)

Description

Erect, herbaceous, winter annual forb with a well developed, 

stout taproot, 4 to 46 inches tall; simple to many branched, especially 

above.

Leaves: Green leaves pinnately lobed to lyrate-pinnatifid with 

8 to 14 pairs of lobes, basal leaves having more than 3 pairs; lower 

leaves petiolate, pinnately lobed to lyrate-pinnatifid, 3 to 22 inches 

long, margins serrate-dentate, tapered base; hirsute with stiff, white 

hairs, especially lower surfaces along midrib, veins, and margin; 

usually forming rosettes; somewhat persistent; upper leaves reduced, 

short petiolate to sessile, oblong to linear, base tapered, uppermost 

leaves bract-like.

Flowers: Flowers December to May; flowering inflorescences 

can range from 4 to 40 inches in height; inflorescences consist of 

anywhere from 6 to 20 flowers; flowers small, dull yellow, making 

them inconspicuous; petals consist of two pairs (cross-like shape), 

generally 1/4 inch wide by 1/8 inch long.

Fruit: Fruit are siliques, 1-1/4 to 2-9/16 inches long with an 

obvious beak at the tip of the pod; pods contain 14 to 30 very small 

red seeds.

Habitat

Especially common in areas with windblown sediments and 

disturbed sites in desert grasslands, desert scrub, and roadsides 

within elevations that generally range below 2,600 feet.

Propagation/Phenology

Reproduces by seed; single plant can produce 750 to 9,000 

seeds.

Comments

Native to the Mediterranean region; Saharan mustard appears to 

suppress native wildflowers by monopolizing available soil moisture 

as it builds canopy and matures seed long before many native species 

have begun to flower. New Mexico Watch List species.
Yellow Flowered Forbs

197

Saharan mustard flowers

© G&AD

Saharan mustard 

rosette 

© JMD

Saharan 

mustard 

downward 

turning 

hairs at base 

of stem

© JMD

Saharan mustard plants

© JMD 
198

Sicilian Starthistle

Centaurea sulphurea Willd. (Aster family, Asteraceae)

Description

Erect, multi-branched winter annual forb to 39 inches tall, with 

spiny or comb-like flower head bracts; taprooted plants exist as 

basal rosettes until erect, simple to highly branched flowering stems 

produced in late spring/summer.

Leaves: Stem leaves alternate, mostly linear or narrowly oblong 

to oblanceolate, margins toothed, or wavy; leaf bases extend down 

the stems and give stems a winged appearance; largest stem wings 

usually 1/4 to 5/16 inch wide; foliage yellowish-green, sparsely 

covered with stiff hairs.

Flowers: Flowers May to July; heads ovoid, spiny, solitary on 

stem tips, consist of numerous yellow 1 to 1-1/2 inch flowers; flower 

head bracts palmately spined, with one long central spine and three 

to five pairs of short lateral spines; glabrous; central spine 1/2 to 1 

inch long, stout, yellowish to straw-colored at tip blackish to dark 

brown near base.

Fruit: Achenes barrel-shaped, compressed, laterally notched 

at the base, 1/4 to 3/8 inch long, glossy dark brown with faint tan 

stripes, bases deeply notched, narrow, broad, hook-like; pappus 

bristles dark brown to black, 1/4 to 5/16 inch long.

Habitat

Cultivated and disturbed or degraded sites in grassland and 

woodland communities, and roadsides within elevations that 

generally range below 3,300 feet.

Propagation/Phenology

Reproduces by seed, seeds fall near the parent plant or are 

dispersed to short distances with wind and to greater distances with 

human activities, animals, water, and soil movement; most seeds 

germinate after the first fall rains; plants exist as basal rosettes 

through winter and early spring until flowering stems develop in late 

spring or early summer.
Yellow Flowered Forbs

199

Sicilian starthistle 

basal rosette

© CDFA

Sicilian starthistle 

flower heads

© DD

Comments

Native to Europe; Sicilian starthistle is a very competitive 

and aggressive plant with allelopathic effects; stands of 

Sicilian starthistle may persist indefinitely once established. 

Arizona prohibited noxious weed.

Sicilian starthistle 

flower heads, 

stems, and foliage

© GFH

Sicilian starthistle flower head

© TF
200

Spiny Sowthistle

Sonchus asper (L.) Hill (Aster family, Asteraceae)

Description

Spiny sowthistle is a taprooted, unbranched or branched, erect 

annual, or biennial that may reach 6 feet in height with bluish-green 

foliage. Stems are pentagonal in cross section and contain a milky 

sap.

Leaves: First leaves are egg shaped, approximately 1/8 to 5/16 

inch long, and occur on petioles; young leaves form a basal rosette 

and have a whitish coating; older leaves alternate, from 2-1/2 to 12 

inches long, 1/2 to 6 inches wide; deep shiny green above, glaucous 

below; generally hairless, egg shaped in outline and have undulating 

prickly margins; leaves on the flowering stem are alternate and have 

rounded lobes that clasp the stem; leaves contain a milky sap.

Flowers: Flowers May to October; yellow flowers occur in loose 

clusters at the ends of stems; flowers range from 1/2 to 1 inch in 

diameter, vase shaped.

Fruit: Fruit is an achene approximately 3/16 inch long, brown, 

wrinkled; mature seed have a white feathery pappus that collectively 

form a white orb similar to dandelion.

Habitat

Equally likely to occur in wetlands or nonwetlands; waste 

ground, disturbed sites, roadsides, and riparian areas within 

elevations that generally range below 8,900 feet.

Propagation/Phenology

Reproduces by seed; as many as 23,000 seeds can be produced 

per plant.

Comments

Native to Eurasia and North Africa; because of the long pappus 

on the fruit, spiny sowthistle can spread easily and quickly become 

established. Spiny sowthistle is somewhat variable in appearance 

because its leaves may be lobed or unlobed along the margins. 

This species generally occurs as a weed in wildland areas of the 

Southwestern Region rather than as an invasive plant. 
Yellow Flowered Forbs

201

Spiny sowthistle flower 

heads and immature 

flower heads

© SD

Spiny sowthistle foliage

© SD

Spiny sowthistle flower head, 

mature flower heads, and 

immature flower heads

© JHM2

Spiny sowthistle 

flower heads and 

foliage (below)

© CE
202

Tansy Ragwort

Senecio jacobaea L. (Aster family, Asteraceae)

Description

Erect, yellow-flowered herbaceous biennial, perennial, or winter 

annual, taprooted, with alternate, pinnately lobed leaves; stems single 

or branched from the root crown to 5 feet tall.

Leaves: Foliage glabrous to lightly covered with long, wavy to 

cottony hairs, especially along midveins and on lower leaf surfaces 

and new growth; leaves highly variable evenly spaced on stems; lower 

leaves taper into indistinct petioles; upper leaves reduced, clasp stem; 

leaves deeply 1- or 2-pinnately dissected, mostly 2 to 8 inches long.

Flowers: Flowers July to September; showy yellow flower heads 

are numerous (20 to 60) in dense flat-topped clusters; flower heads are 

less than 1 inch across, ray flowers number 10 to 13, 5/16 to 1/2 inch 

long; flower head bracts are very small, 1/8 to 3/16 inch long, often 

with a black tip.

Fruit: Achenes cylindrical with shallow ribs, 1/16 to 1/8 inch 

long, light brown, often pubescent; pappus bristles numerous, soft, 

white, about twice the achenes’ length; ray flower achenes glabrous 

with deciduous pappus, disk flower achenes pubescent on ribs, with 

persistent pappus.

Habitat

Cultivated and disturbed or degraded moist sites in meadows, 

grassland, woodland, and riparian communities, and roadsides; grows 

best on light, well-drained soils within elevations that generally range 

below 4,900 feet.

Propagation/Phenology

Reproduces by seed and vegetatively from roots; seeds can remain 

viable for at least 6 years under field conditions; root crowns and 

roots can develop new root and shoot buds, especially in response to 

disturbance or injury; root fragments can produce new shoots.

Comments

Native to Eurasia; tansy ragwort is an aggressive species and 

is highly poisonous to cattle, horses, and goats. Arizona prohibited 

noxious weed.
Yellow Flowered Forbs

203

Tansy ragwort 

plants

© FD

Tansy ragwort flower heads 

(below)

© MS

Tansy ragwort fruit

© LJM

Tansy ragwort plants

© RO
204

Texas Blueweed

Helianthus ciliaris DC. (Aster family, Asteraceae)

Description

Erect perennial forb 1 to 2 feet tall, with bluish-green foliage and 

woody creeping roots; new shoots arising from root buds often create 

dense patches; plant has a strong pungent odor, especially when 

crushed.

Leaves: The sessile leaves are typically glabrous or hairy on the 

margins, sessile, bluish-green, covered with a whitish film, mostly 

opposite, oblong to lanceolate, 1-1/16 to 4 inches long; margins are 

wavy, entire to shallowly lobed; stems often sparsely covered with 

short stiff hairs.

Flowers: Flowers June to November; showy composite flower 

heads solitary on long peduncles; flower head receptacles 9/16 to 1 

inch across; group of disk flowers rounded on top, yellowish; yellow 

ray flower corollas about 3/8 inch long; disk flower corollas about 

3/16 inch long with red lobes; receptacle chaffy bracts hairy at the 

tips, entire or 3-lobed.

Fruit: Similar to those of commercial sunflower; however, 

achenes much smaller, about 1/8 inch long; pappus scales 2 to 4, 

about 1/16 inch long.

Habitat

Cultivated and disturbed or degraded moist open sites in 

meadows, grassland, woodland, forest, and riparian communities and 

roadsides; grows best on alkaline or saline soils within elevations 

that generally range from 3,000 to 8,500 feet.

Propagation/Phenology

Reproduces by vegetative clones from root buds and by seed; 

seed viability is often low, about 1 percent.

Comments

Texas blueweed is an aggressive perennial sunflower that is 

native to the grasslands of the south central United States. It naturally 

persists in low densities in native grasslands, but thrives in cultivated 

or heavily disturbed areas. Arizona prohibited/restricted noxious 

weed.
Yellow Flowered Forbs

205

Texas blueweed 

flower head (below)

© RET

Texas blueweed 

flower head 

bracts

© RET

Texas blueweed plants

© RET

Texas blueweed plants (above)

© RET
206

Wild Mustard

Sinapis arvensis L. (Mustard family, Brassicaceae)

Description

Erect winter annual, taprooted forb, 8 to 39 inches tall; stems 

branched and striated, with coarse spreading hairs especially near the 

base; upper stems terminate in narrow racemes of yellow flowers.

Leaves: All leaves bristly; basal leaves petiolate (3/8 to 1-9/16 

inches long), oblong, oval, lanceolate, lyrate, pinnatifid to dentate, 

1-9/16 to 7-1/8 inches long, 3/4 to 2 inches wide; upper leaves much 

reduced, simple, and short petiolate to sessile but not auriculate 

clasping.

Flowers: Flowers March to October; racemes of stalked, bright 

yellow flowers; flowers 3/8 to 3/4 inch across, consisting of 4 sepal, 

and 4 yellow petals; sepals yellow or green, 3/16 to 9/32 inch long, 

and less than 3/32 inch wide, spreading at various angles, usually 

some downturned or horizontal, not appressed to the petal tube; 

petals are well rounded toward their tips, 5/16 to 11/16 inch long, and 

1/8 to 5/16 inch wide.

Fruit: Fruit is a silique, 1-3/16 to 2 inches long with a beak 3/8 

to 3/4 inch long that is flattened-quadrangular, valves of silique are 

glabrous or rarely bristly, three to five nerved; seeds smooth, less 

than 1/16 inch in diameter, reddish brown to black.

Habitat

Wild mustard occurs in dry disturbed sites such as waste places, 

pastures, and along roadsides and railroad rights-of-way within 

elevations that generally range below 6,000 feet.

Propagation/Phenology

Reproduces by seed.

Comments

Native to Eurasia; wild mustard seeds and the foliage have a 

pungent taste. Wild mustard grows profusely and contains chemicals 

of the class glucosinolates, including sinalbin; however, the leaves 

are edible at the juvenile stage of the plant. This species generally 

occurs as a weed in wildland areas of the Southwestern Region rather 

than as an invasive plant.
Yellow Flowered Forbs

207

Wild mustard flowers (above)

© BA

Wild mustard plant(s)

© LR

Wild mustard stems (below)

© LR

Wild mustard fruit

© JMD
208

Wooly Mullein

Verbascum thapsus L. (Figwort family, Schrophulariaceae)

Description

Biennial forb; during first year, plant consists of a rosette of basal 

leaves about 1 to 2 feet across; during second year, flowering stalk 

grows to 3 to 7 feet tall, usually unbranched; occasionally, one or 

two side stems may develop in the upper half of the plant; foliage is 

covered with downy white hairs.

Leaves: Leaves, thick, alternate up to 12 inches long and 4 inches 

wide, becoming progressively smaller and narrower as they ascend 

the central stem; obovate or oblong-ovate in shape, smooth or slightly 

crenate along the margins; covered with fine downy hairs; lower leaves 

taper gradually to a narrow winged base; upper leaves are partially 

wrapped or have wings around the stem or petiole and extend down 

along the stem; dense branched hairs provide the foliage with a color 

that is whitish or greyish green.

Flowers: Flowers June to August; flowering stalk ends in a dense 

spike of pale yellow 5-petalled flowers about 1/2 to 2 inches long 

and 3/4 of an inch across; 5 green sepals hairy; flowering starts at the 

bottom of the spike and progresses irregularly upward; only a few 

flowers are in bloom at a time.

Fruit: Plants produce small ovoid capsules less than 1/4 inch long 

that split in half; each capsule contains large numbers of minute brown 

seeds less than a 1/16 of an inch in size, marked with longitudinal 

ridges.

Habitat

Cultivated and disturbed or degraded sites in meadows, grassland, 

woodland, chaparral, forest, and riparian communities, and roadsides 

within elevations that generally range from 3,500 to 10,000 feet.

Propagation/Phenology

Reproduces by seed; the plant is an extremely prolific seed bearer, 

a single plant may produce hundreds of capsules, each containing up to 

700 or more seeds; up to 180,000 or 240,000 seeds total.

Comments

Native to Eurasia and Africa; once established, wooly mullein 

grows more vigorously than many native species; its growth can 
Yellow Flowered Forbs

209

Wooly mullein flowers

© MEH

Wooly mullein plants

© SD

overtake a site in short order. It is a prolific seeder and its seeds 

last a very long time in the soil; an established population of 

wooly mullein can be extremely difficult to eradicate. Rosettes 

of wooly mullein may be confused with Mediterranean sage 

rosettes. This species generally occurs as a weed in wildland 

areas of the Southwestern Region rather than as an invasive 

plant.

Wooly mullein foliage (left)

© CM

Wooly mullein basal rosette (above)

© F&KS
210

Yellow Salsify

Tragopogon dubius Scop. (Aster family, Asteraceae)

Description

Yellow salsify is an erect, branched, annual, biennial, or short-lived 

perennial forb, 12 to 39 inches tall with milky sap. Taproots are stout, 

fleshy, thick, and long. In its first year(s), yellow salsify produces an 

erect rosette of grasslike leaves. Plants may remain vegetative for up to 

10 years before flowering; after flowering, the plant dies.

Leaves: Leaves are alternate, clasping, linear, and grasslike with 

straight, pointed tips; mostly glabrous but with some loose, wooly hairs 

in the axils; 4 to 12 inches long and roughly 1/4 inch wide.

Flowers: Flowers May to September; inflorescence a single head 

on a long stalk, enlarged and hollow under the heads; heads solitary at 

the ends of branches, 1-1/2 inches wide with pale yellow ray flowers, 

bracts longer than the rays; involucral bracts in a single series, equal, 

about 13 in number, 15/16 to 1-9/16 inches long in flower, distinctly 

surpassing the pale, lemon-yellow, ligulate corollas, elongating to 

1-9/16 to 2-3/4 inches long in fruit; pappus of a single series of whitish, 

uneven length, plumose bristles.

Fruit: Achenes slender, 15/16 to 1-7/16 inches long, gradually 

narrowed to a stout beak; mature seed have a white feathery pappus 

and may reach 4 inches long; collectively form a white orb similar to 

dandelion but much larger.

Habitat

Given a seed source and a canopy opening, yellow salsify is a 

potential inhabitant of nearly any vegetation or community type within 

elevations that generally range from 4,500 to 8,500 feet.

Propagation/Phenology

Reproduces by seed. 

Comments

Native to southern and central Europe and western Asia; disturbed 

sites are common yellow salsify habitats, but persistence on disturbed 

sites is indefinite, and long distance seed dispersal from disturbed 

sites into relatively open, undisturbed sites is common. This species 

generally occurs as a weed in wildland areas of the Southwestern 

Region rather than as an invasive plant.
Yellow Flowered Forbs

211

Yellow salsify mature 

flower head (below)

© SD

Yellow salsify 

flower head (below)

© JC

Yellow salsify stems 

and foliage

© TW

Yellow salsify plant with 

immature and mature 

flower heads

© WMC
212

Yellow Starthistle

Centaurea solstitialis L. (Aster family, Asteraceae)

Description

Erect, multi-branched annual (sometimes biennial) forb, to 6-1/2 

feet tall, with spiny flower head bracts; stoutly taprooted plants exist 

as basal rosettes until erect, highly branched flowering stems are 

produced in late spring/summer.

Leaves: Stem leaves alternate, mostly linear or narrowly oblong 

to oblanceolate; margins smooth, toothed, or wavy; leaf bases extend 

down the stems and give stems a winged appearance; largest stem 

wings typically to 3/16 inch wide; lower stem leaves sometimes 

deeply pinnate-lobed; foliage grayish- to bluish-green, densely 

covered with fine white cottony hairs that partially hide thick stiff 

hairs and resinous dots. 

Flowers: Flowers May to December; heads ovoid, spiny, solitary 

on stem tips, consist of numerous yellow 5/8 to 3/4 inch flowers; 

flower head bracts palmately spined, with one long central spine and 

two to three pairs of short lateral spines; bracts dense to sparsely 

covered with cottony hairs or with patches at the spine bases; 

central spine 1/2 to 1 inch long, stout, yellowish to straw-colored 

throughout.

Fruit: Two types of achenes, both glabrous, less than 3/16 

inch long, with broad bases; outer achenes dull dark brown, often 

speckled with tan, lack pappus bristles, inner achenes glossy, gray 

or tan to mottled cream-colored and tan, with slender white pappus 

bristles 1/8 to 1/4 inch long.

Habitat

Cultivated and disturbed or degraded sites in grassland, forest, 

and woodland communities, and roadsides within elevations that 

generally range below 8,200 feet.

Propagation/Phenology

Reproduces by seed, up to 75,000 per plant; seed germination is 

closely correlated with rainfall events; can survive for up to 10 years, 

depending on environmental conditions.
Yellow Flowered Forbs

213

Yellow starthistle flower heads

© SD

Yellow starthistle flower heads 

and stems

© BR

Yellow starthistle 

winged stem 

margins (right)

© SD

Yellow starthistle plant

© CR

Comments

Native to southern Europe; yellow starthistle plants are 

highly competitive and typically develop dense, impenetrable 

stands that displace other vegetation; yellow starthistle looks 

very similar to Malta starthistle. Arizona prohibited/restricted 

noxious weed and New Mexico Class A noxious weed.
214

Yellow Sweetclover 

Melilotus officinalis (L.) (Pea family, Fabaceae)

Description

Taprooted, erect, branched, annual, biennial or short-lived 

perennial forb, 2 to 7 feet tall; larger plants branch frequently and 

are somewhat bushy in appearance, while shorter plants are less 

branched and rather lanky; stems are glabrous, furrowed, and 

angular; sometimes the lower stems are ribbed light red.

Leaves: The alternate compound leaves are trifoliate (cloverlike) and hairless; each leaflet is about 3/4 inch long and 1/4 inch 

wide, oblong, oblanceolate, or obovate in shape, and dentate along 

the middle or upper margin; terminal leaflet has a short stalk at its 

base, while the lateral leaflets are nearly sessile; petiole of each 

compound leaf is about 1/2 inch long; there are a pair of small linear 

stipules at its base.

Flowers: Flowers April to September; spike-like racemes of 

yellow flowers are abundantly produced; each raceme is up to 6 

inches long and has dozens of yellow to cream-colored flowers; 

flowers about 5/16 inch long; when fully open, it has a pea-like floral 

structure with an upper standard and lower keel.

Fruit: Fruit is a small seedpod, less than 3/16 inch long, crossribbed and contains one to two seeds; seeds are tannish-yellow and 

somewhat flattened and kidney-shaped.

Habitat

Cultivated and disturbed or degraded sites in meadows, 

grassland, woodland, and forest communities, and roadsides within 

elevations that generally range from 5,000 to 10,500 feet.

Propagation/Phenology

Reproduces by seed; well-developed plants may produce more 

than 1,000 seeds.

Comments

Native to Eurasia; yellow sweetclover is very similar to M. 

alba (white sweetclover), which is another weedy species native to 

Eurasia; white sweetclover has white flowers, greyish-green foliage, 

and its slightly reticulated seedpods lack conspicuous cross-ribs; 

otherwise, these two species are nearly identical; USDA Plants 
Yellow Flowered Forbs

215

Yellow sweetclover flowering 

inflorescences

© TH

Yellow sweetclover leaf and fruit

© PTL

Yellow 

sweetclover 

plants

© DP

Database considers them synonymous. This species generally 

occurs as a weed in wildland areas of the Southwestern Region 

rather than as an invasive plant.

Yellow 

sweetclover 

flowers

© SD
216

Yellow Toadflax 

Linaria vulgaris Miller (Figwort family, Scrophulariaceae)

Description

Erect, single or multi-stemmed, clump or patch-forming perennial 

forb; 12 to 24 inches tall, with creeping roots and showy yellow 

flowers; flowers are borne in axils of an elongated dense or open 

raceme, with an erect or drooping tip. 

Leaves: Leaves primarily alternate, but crowded and often 

appearing opposite or whorled, especially near the bases of stems; 

leaf margins entire, sessile, linear, 7/8 to 2 inches long; soft, mostly 

spreading to drooping, glabrous or sparsely covered with long soft 

hairs.

Flowers: Flowers May to September. Flowers showy, bright 

yellow (sometimes white), snapdragon-like, 2-lipped, 5-lobed, with 

a long, straight, downward pointing spur near the base of the lower 

corolla tube; 1-3/8 to 2-1/8 inches long, including spur; throat and 

lower lip orange-hairy.

Fruit: Round, 2-chambered capsule, 3/8 to 1/2 inch long; opening 

by irregular slits at the apex to release numerous black to brown, 1/16 

to 1/8 inch in diameter, flattened with circular or papery winged seeds.

Habitat

Cultivated and disturbed or degraded sites in meadows, grassland, 

woodland, and riparian communities, and roadsides within elevations 

that generally range from 6,400 to 9,200 feet.

Propagation/Phenology

Reproduces by seed (up to 30,000) and vegetatively from creeping 

lateral roots; plants develop an extensive system of vertical and lateral 

roots that produce new shoots; root fragments can produce new plants; 

plants can rapidly colonize a site by vegetative reproduction from 

creeping roots. 

Comments

Native to southeast Eurasia; germination is highest on open sites 

with compacted soils and little vegetation; an extensive root system 

makes this plant difficult to control; yellow toadflax and Dalmatian 

toadflax can hybridize. New Mexico Class A noxious weed.
Yellow Flowered Forbs

217

Yellow toadflax flowers

© RO

Yellow toadflax 

flowers

© SD

Yellow toadflax flowers and foliage

© MS

Yellow toadflax 

plants

© MS
218

Photography Credits

I would like to thank all of the individuals and/or organizations 

who so graciously granted permission and allowed the use of their 

photographs; they are accredited under each individual photograph 

used in this booklet and listed below.

© AD: Photo Courtesy of Ann Dennis, 2002 @ calphotos.

berkeley.edu — burclover 

© AF: Photo Courtesy of Alison Fox, University of Florida, 

Bugwood.org — Eurasian watermilfoil

© AS: Photo Courtesy of Al Schneider @ USDA-NRCS 

PLANTS Database — blue mustard

© ASUH: Photo Courtesy of Arizona State University Herbarium 

— Arabiangrass

© AV: Photo Courtesy of Anthony Valois and the Santa Monica 

Mountains National Recreation Area, USDI National 

Park Service — chicory

© BA: Photo Courtesy of Bruce Ackley, The Ohio State 

University, Bugwood.org — spiny sowthistle, wild 

mustard

© BB: Photo Courtesy of Barry Breckling, 2010 @ calphotos.

berkeley.edu — floating primrose-willow

© B&LC: Photo Courtesy of Barbara J. and Lorence G. Collins, 

Thousand Oaks, CA @ www.clunet.edu/gf — African 

sumac

© BM: Photo Courtesy of Bonnie Million, National Park 

Service, Bugwood.org — curveseed butterwort,

Dalmatian toadflax, halogeton, redstem filaree, Russian 

knapweed, saltcedar, Scotch thistle 

© BR: Photo Courtesy of Barry Rice, sarracenia.com, 

Bugwood.org — chicory, Johnsongrass, purple 

starthistle, spiny cocklebur, teasel, whitetop, yellow 

starthistle

© CB: Photo Courtesy of Chuck Bargeron, University of 

Georgia, Bugwood.org — tree of heaven
219

© CDFA: Photo Courtesy of Staff CDFA, California Dept. of Food 

& Agriculture, Integrated Pest Control Branch, 2001 @ 

calphotos.berkeley.edu — Iberian knapweed, Sicilian 

starthistle

© CE: Photo Courtesy of Chris Evans, River to River CWMA, 

Bugwood.org — bull thistle, cheatgrass, giant reed, 

Russian olive, spiny sowthistle, whitetop 

© CM: Photo Courtesy of Carey Minteer, University of Georgia, 

Bugwood.org — wooly mullein

© CR: Photo Courtesy of Cindy Roche, Bugwood.org — 

meadow knapweed, yellow starthistle

© CS: Photo Courtesy of Clinton Shock, Oregon State 

University, Bugwood.org — halogeton

© CTB: Photo Courtesy of Charles T. Bryson, USDA 

Agricultural Research Service, Bugwood.org — 

Johnsongrass

© DB: Photo Courtesy of Douglas Barbe, California 

Department of Food and Agriculture, Bugwood.org — 

African rue

© DC: Photo Courtesy of David Cappaert, Michigan State 

University, Bugwood.org — perennial sowthistle

© DD: Photo Courtesy of D. Dixon, California Dept. of Food 

& Agriculture, Integrated Pest Control Branch, 2001 @ 

calphotos.berkeley.edu — Sicilian starthistle

© DJM: Photo Courtesy of David J. Moorhead, University of 

Georgia, Bugwood.org — giant reed

© DP: Photo Courtesy of Dave Powell, USDA Forest Service, 

Bugwood.org — yellow sweetclover

© DWT: Photo Courtesy of Dean Wm. Taylor, 1980 @ calphotos.

berkeley.edu — curveseed butterwort

© EB: Photo Courtesy of Elizabeth Bella, USDA Forest 

Service, Bugwood.org — white sweetclover
220

© EC: Photo Courtesy of Eric Coombs, Oregon Department 

of Agriculture, Bugwood.org — meadow knapweed, 

Mediterranean sage, purple loosestrife 

© EL: Photo Courtesy of Eric LHOTE @ L’Atelier Artistique 

du Paysage, 2010, www.latelierartistiquedupaysage.com 

— Mediterranean sage

© EM: Photo Courtesy of Elizabeth Makings @ asu.edu — 

sweet resinbush

© FD: Photo Courtesy of Faith Duncan, USDA Forest Service, 

Bugwood.org — tansy ragwort

© F&KS: Photo Courtesy of Forest & Kim Starr, U.S. Geological 

Survey, Bugwood.org — crimson fountaingrass, 

Himalayan blackberry, little hogweed, parrot feather 

milfoil, puncturevine, red clover, redstem filaree, 

rescuegrass, ripgut brome, Russian thistle, southern 

sandbur, weeping lovegrass, white clover, wooly mullein 

© GAC: Photo Courtesy of G.A. Cooper, USDA-PLANTS 

Database, Bugwood.org — African rue

© G&AD: Photo Courtesy of George and Audrey DeLange@ 

www.delange.org — African sumac, globe chamomile, 

Saharan mustard, white sweetclover

© GAM: Photo Courtesy of Gary A. Monroe @ USDA-NRCS 

PLANTS Database — curveseed butterwort

© GFH: Photo Courtesy of G.F. Hrusa, California Dept. of Food 

& Agriculture, Botany Laboratory, 2001 @ calphotos.

berkeley.edu — Sicilian starthistle

© GH: Photo Courtesy of Gerald Holmes, Valent USA 

Corporation, Bugwood.org — alfalfa

© GL: Photo Courtesy of Graves Lovell, Alabama Department 

of Conservation and Natural Resources, Bugwood.org 

— floating primrose-willow

© GLP: Photo Courtesy of Gary L. Piper, Washington State 

University, Bugwood.org — spiny plumeless thistle
221

© HB: Photo Courtesy of Henry Brisse, @ henry.brisse@univcezanne.fr — sweet resinbush

© HFS: Photo Courtesy of Howard F. Schwartz, Colorado State 

University, Bugwood.org — alfalfa, puncturevine 

© HZ: Photo Courtesy of H. Zell, 12 August 2009, Wikimedia 

Commons, http://en.wikipedia.org/wiki/File:Vitex_

agnus-castus — lilac chastetree

© JB: Photo Courtesy of Joseph Berger, Bugwood.org — 

redstem filaree

© JC: Photo Courtesy of John Cardina, the Ohio State 

University, Bugwood.org — Johnsongrass, spotted 

knapweed, yellow salsify

© JCS: Photo Courtesy of J. C. Schou @ Biopix — field brome

© JDB: Photo Courtesy of John D. Byrd, Mississippi State 

University, Bugwood.org — poison hemlock

© JHM1: Photo Courtesy of James H. Miller, USDA Forest 

Service, Bugwood.org — giant reed, weeping lovegrass

© JHM2: Photo Courtesy of James H. Miller @ USDA-NRCS 

PLANTS Database/James H. Miller and Karl V. Miller. 

2005. Forest plants of the southeast and their wildlife 

uses. University of Georgia Press, Athens — spiny 

sowthistle

© JHM&TB: Photo Courtesy of James H. Miller & Ted Bodner, 

Southern Weed Science Society, Bugwood.org — tall 

fescue, tall morning-glory

© JMD: Photo Courtesy of Joseph M. DiTomaso, University 

of California - Davis, Bugwood.org — African rue, 

Arabiangrass, buffelgrass, diffuse knapweed, Dyer’s 

woad, field brome, field sandbur, hairy whitetop, 

Lehmann lovegrass, lens-podded hoarycress, Malta 

starthistle, Mediterranean grass, ravennagrass, 

rescuegrass, ripgut brome, rush skeletonweed, Saharan 
222

mustard, squarrose knapweed, tall fescue, Uruguayan 

pampas grass, weeping lovegrass, whitetop, wild 

mustard

© JMR: Photo Courtesy of John M. Randall, the Nature 

Conservancy, Bugwood.org — buffelgrass, camelthorn, 

Canada thistle, crimson fountaingrass, Himalayan 

blackberry, hounds-tongue, kochia, leafy spurge, 

Lehmann lovegrass, Malta starthistle, red brome, 

Russian knapweed, saltcedar, Siberian elm, spiny 

cocklebur 

© JN: Photo Courtesy of Jamie Nielsen, University of Alaska 

Fairbanks, Cooperative Extension Service, Bugwood.org 

— white sweetclover

© JS: Photo Courtesy of Jan Samanek, State Phytosanitary 

Administration, Bugwood.org — black henbane, 

common cocklebur, poison hemlock, tree of heaven

© JV: Photo Courtesy of Joy Viola, Northeastern University, 

Bugwood.org — Uruguayan pampas grass

© KAR: Photo Courtesy of Karan A. Rawlins, University of 

Georgia, Bugwood.org — black medick, horehound

© KW: Photo Courtesy of Keith Weller, USDA Agricultural 

Research Service @ bugwood.org — alfalfa

© LA: Photo Courtesy of Lloyd Andres, USDA Agricultural 

Research Service, Bugwood.org — Mediterranean sage

© LJM: Photo Courtesy of Leslie J. Mehrhoff, University of 

Connecticut, Bugwood.org — Eurasian watermilfoil, 

tansy ragwort

© LLB: Photo Courtesy of L.L. Berry, Bugwood.org — 

Mediterranean sage

© LM: Photo Courtesy of Liz Marking @ http://swbiodiversity.

org/seinet — globe chamomile 
223

© LR: Photo Courtesy of Luigi Rignanese, 2005, 2007 

@ calphotos.berkeley.edu — bigleaf periwinkle, 

horehound, kochia, onionweed, perennial wallrocket, 

teasel, wild mustard

© LTK: Photo Courtesy of Loke T. Kok, Virginia Polytechnic 

Institute and State University, Bugwood.org — musk 

thistle

© LW: Photo Courtesy of Linda Wilson, University of Idaho, 

Bugwood.org — Dalmatian toadflax

© MEH: Photo Courtesy of Mary Ellen (Mel) Harte, Bugwood.

org — black henbane, broadleaved pepperweed, 

common burdock, field bindweed, hairy whitetop, 

hounds-tongue, lens-podded hoarycress, musk thistle, 

oxeye daisy, Russian thistle, wooly mullein

© ML: Photo Courtesy of Max Licher @ http://swbiodiversity.

org/seinet — bigleaf periwinkle, blue mustard, Malta 

starthistle

© MS: Photo Courtesy of Michael Shephard, USDA Forest 

Service, Bugwood.org — bull thistle, perennial 

sowthistle, tansy ragwort, yellow toadflax 

© NER: Photo Courtesy of Norman E. Rees, USDA Agricultural 

Research Service, Bugwood.org — diffuse knapweed, 

purple loosestrife

© NL: Photo Courtesy of Nancy Loewenstein, Auburn 

University, Bugwood.org — parrot feather milfoil

© OSWL: Photo Courtesy of Ohio State Weed Lab Archive, 

the Ohio State University, Bugwood.org — Carolina 

horsenettle, Johnsongrass, quackgrass, spotted knapweed

© PB: Photo Courtesy of Patrick Breen, Oregon State 

University, Bugwood.org — Russian olive

© PEB: Photo Courtesy of Paul E. Berry, Wisconsin State 

Herbarium, University of Wisconsin-Madison — white 

sweetclover
224

© PF: Photo Courtesy of Patti Fenner, Tonto National Forest, 

USDA Forest Service — African sheepbush

© PJA: Photo Courtesy of Patrick J. Alexander @ USDA-NRCS 

PLANTS Database — black medic, tall morning-glory, 

white clover 

© PTL: Photo Courtesy of Pedro Tenorio-Lezama, Bugwood.

org — broadleaved pepperweed, oxeye daisy, Russian 

thistle, tall morning-glory, yellow sweetclover

© PW1: Photo Courtesy of Phil Westra, Colorado State 

University, Bugwood.org — common cocklebur, little 

hogweed

© PW2: Photo Courtesy of Paul Wray, Iowa State University, 

Bugwood.org — Russian olive, tree of heaven

© RAH: Photo Courtesy of R.A. Howard @ USDA-NRCS 

PLANTS Database — chicory

© RET: Photo Courtesy of Ruth E. Timme, Research Assistant, 

University of Maryland @ www.ruthtimme.com — 

Texas blueweed

© RHM: Robert H. Mohlenbrock, @ USDA-NRCS PLANTS 

Database — black medick

© RL: Photo Courtesy of Ricky Layson, Ricky Layson 

Photography, Bugwood.org — musk thistle

© RO: Photo Courtesy of Richard Old, XID Services, Inc., 

Bugwood.org — alfalfa, blue mustard, common 

burdock, crimson fountaingrass, diffuse knapweed, 

Eurasian watermilfoil, field sandbur, hairy whitetop, 

Himalayan blackberry, kochia, Mediterranean grass, red 

clover, redstem filaree, rush skeletonweed, Siberian elm, 

southern sandbur, tansy ragwort, tree of heaven, wild 

oat, yellow toadflax

© RRB: Photo Courtesy of Robin R. Buckallew @ USDA-NRCS 

PLANTS Database — tall morning-glory
225

© RS: Photo Courtesy of Richard Spellenberg, 2012 @ 

calphotos.berkeley.edu — globe chamomile

© RV: Photo Courtesy of Robert Vidéki, Doronicum Kft., 

Bugwood.org — chicory, common cocklebur, houndstongue, Scotch thistle, spiny cocklebur

© SD: Photo Courtesy of Steve Dewey, Utah State University, 

Bugwood.org — black henbane, broadleaved 

pepperweed, bull thistle, camelthorn, Canada thistle, 

cheatgrass, diffuse knapweed, Dyer’s woad, jointed 

goatgrass, leafy spurge, musk thistle, oxeye daisy, 

perennial sowthistle, purple loosestrife, purple 

starthistle, quackgrass, rush skeletonweed, Russian 

knapweed, saltcedar, Scotch thistle, spiny sowthistle, 

spotted knapweed, squarrose knapweed, teasel, wild oat, 

wooly mullein, yellow salsify, yellow starthistle, yellow 

sweetclover, yellow toadflax

© SH: Photo Courtesy of Steve Hurst @ USDA-NRCS 

PLANTS Database — Arabiangrass, Mediterranean 

grass

© SM: Photo Courtesy of Steve Matson, 2005 @ calphotos.

berkeley.edu — burclover, lens-podded hoarycress, wild 

oat

© ST: Photo Courtesy of Steve Thorsted, 2010 @ calphotos.

berkeley.edu — onionweed

© TB: Photo Courtesy of Ted Bodner, Southern Weed Science 

Society, Bugwood.org — Carolina horsenettle

© TF: Photo Courtesy of T. Fuller, California Dept. of Food 

& Agriculture, Botany Laboratory, 2001 @ calphotos.

berkeley.edu — Sicilian starthistle

© TH: Photo Courtesy of Tom Heutte, USDA Forest Service, 

Bugwood.org — field bindweed, perennial sowthistle, 

red clover, yellow sweetclover

© TNC: Photo Courtesy of the Nature Conservancy, 2000 @ 

tncweeds.ucdavis.edu — lens-podded hoarycress
226

© TP: Photo Courtesy of Todd Pfeiffer, Klamath County Weed 

Control, Bugwood.org — spiny plumeless thistle

© TW: Photo Courtesy of Theodore Webster, USDA 

Agricultural Research Service, Bugwood.org — yellow 

salsify

© USDA1: Photo Courtesy of USDA APHIS PPQ Archive, USDA 

APHIS PPQ, Bugwood.org — jointed goatgrass, leafy 

spurge, onionweed

© USDA2: Photo Courtesy of USDA NRCS Archive, USDA NRCS, 

Bugwood.org — Siberian elm

© USU: Photo Courtesy of Utah State University Archive, Utah 

State University, Bugwood.org — Dalmatian toadflax, 

little hogweed, puncturevine, rush skeletonweed 

© V: Photo Courtesy of Vilseskogen at http://www.flickr.com/

photos/vilseskogen/3066876182/ and http://www.flickr.

com/photos/vilseskogen/3066035257/ — parrot feather 

milfoil

© WMC: Photo Courtesy of William M. Ciesla, Forest Health 

Management International, Bugwood.org — yellow 

salsify

© X: Photo Courtesy of Xenomorf, 2006 @ Dave’s Gargen.

com — African sumac, globe chamomile
227

“A weed is a plant whose 

virtues have not yet been 

discovered.”

 — Ralph Waldo Emerson