Invasive Weeds

of the Tahoe National Forest

A Comparison Guide 

to Non-native Invasive Plants and Common Look-alikes
1

Graphic Design & Illustrations

Annaliese Miller

Photography courtesy of:

Jim Belsher-Howe, Robin Breckenridge, Beth Brenneman, 

Laura Ann Eliassen, Joe DiTomaso, Susan Donaldson, 

Louis Landry, Steve Matson, Annaliese Miller, 

Gary Monroe, Keir Morse, Tamara Sasaki, Susi Urie, 

Kathy VanZuuk, Charles Webber, Kathy Welch

Text

Susan Donaldson, Susi Urie

United States Forest Service Publication

R5-TP-024, 2013

Tahoe National Forest

Produced in cooperation with the USDA Forest Service, which is an equal 

opportunity service provider and employer.

Adapted with permission from “Invasive Weeds of the 

Lake Tahoe Basin”, S. Donaldson, University of Nevada 

Cooperative Extension SP-09-06 copyright 2009.

Illustrations © 2013, Annaliese Miller 

Contact her at: aninau.com, amtahoe@gmail.com

Invasive Weeds

of the Tahoe National Forest

A Comparison Guide to 

Non-native Invasive Plants and Common Look-alikes
2 3

Invasive Weeds

of the Tahoe National Forest

Non-native invasive plants are aggressive plants that have 

been introduced into an environment outside of their native 

range. Sometimes referred to as alien species, these invasive 

weeds have been separated from the natural enemies that 

help control them in their homeland. 

They grow rapidly, reproduce profusely, and compete with 

native plants for water, light and nutrients. Some of these 

weeds have been designated as noxious by California and 

Nevada law, requiring control efforts by property owners 

(See Page 5).

Non-native invasive plants tend to outcompete native plants, 

especially where lands have been disturbed. When they 

displace native plants and animals, they lower diversity, 

reduce hunting and fishing potential, change the aesthetics 

of a habitat, inhibit recreational activities and tourism, crowd 

out endangered species, and reduce forage value. Along 

the Truckee River, weeds that have coarse or shallow root 

systems, such as perennial pepperweed and Dalmatian 

toadflax, increase soil erosion and threaten water clarity.

The Truckee River Weed Warriors, formed by the Truckee 

River Watershed Council in 2010, raise awareness about 

local non-native invasive plants, involve volunteers in their 

control, and report rated noxious weeds appropriately to 

partners for treatment.

If you find an invasive weed, please report the infestation 

to “Report a Weed” on www.truckeeriverwc.org or your 

local County Agricultural Department when outside the 

Truckee River watershed.

How to Use the Guidebook

This guidebook will help you identify the invasive plants 

threatening the Tahoe National Forest and surrounding 

areas. Compare invasive plants with common “look-alikes” 

to help you differentiate between desirable native plants 

and non-native invasive plants. 

Look for these face icons at the top of the page: 

	= Non-native invasive plants

 = Desirable Look-alikes (native and non-invasive)

 = Plants that could potentially become invasive.

 (You may choose to avoid planting species that 

 may become invasive on your property.)

Information on management is also included for each 

invasive weed, as is the noxious weed status in California. 

California’s noxious weed rating system designation is based 

on distribution and relative tenacity of the weed. 

“A” rated: very invasive, but have a limited distribution 

throughout the state and are considered top priority 

for control before they become widespread.

“B” rated: very invasive and more widespread. Priority 

of “B” rated weed treatment is decided on a 

case-by-case basis depending on the local value of 

resource being compromised, local distribution, and 

funds available.

“C” rated: generally spread beyond the point where the 

state of California can justify spending limited 

resources, but the private citizen may control them 

on their own.

Relative abundance of each species is also provided.

Widespread: Found at numerous locations in the area

Moderate: Found at several locations; large

populations may occur at a few locations

Infrequent: Only at one or a few locations; no large 

populations
4 5

Preventing the Spread of Weeds

Prevention is the least expensive and most effective way to 

halt the spread of noxious and invasive weeds.

This requires:

	 • Educating workers and the public about the 	 	 	

 importance of managing weeds on an ongoing basis

	 • Properly identifying weed species

	 • Avoiding or treating existing weed populations

	 • Preventing weed seeds or other plant parts from 	 	

 establishing new or bigger populations 

Steps you can take:

1. Use this book to identify invasive weeds in your area. 

2. Inspect your work or play area. Identify any invasive weeds;

 map the location of the weeds. (See Page 5 for reporting weeds.)

3. Clean vehicles, shovels and other soil-disturbing equipment 

 prior to entering a site to avoid introducing weeds. 

4. Don’t introduce weed-contaminated soil, fill, or other 

 materials to new sites. Use certified weed-free products. 

5. Check shoes, clothing, bicycles and vehicles regularly 

 for weed seeds or other plant parts. Carefully remove 

 and dispose of weedy materials. 

6. Pressure-wash vehicles and equipment after driving 

 in weedy areas. Periodically monitor and treat areas 

 to prevent weedy plants from establishing. 

7. Establish a decontamination area such as a tarp for 

 cleaning clothing and equipment. 

8. Don’t walk, ride or drive through infestations. When 

 operating vehicles, stay on established roads or trails. 

9. If dogs accompany you, check their paws and coats 

 for weed seeds and other plant parts and remove them. 

10. Don’t plant invasive weeds in your garden or landscape. 

11. Get advice for treatment on private property from your 

 local county agriculture department. (See Page 77 for 

 contact information.)

Reporting and Controlling Weeds

“Noxious weed” is a legal term employed by the California 

Dept. of Food and Agriculture, and refers to an invasive plant 

that poses a significant threat to our environment. Noxious 

weeds have been assigned a priority rating of “A”, “B”, or “C” 

according to the current knowledge of state-wide distribution 

(see pp. 2 & 3). 

Report all “A” & “B” rated noxious weeds. 

See the following pages for plant descriptions and directions. 

Visit www.truckeeriverwc.org to report these invasive plants. 

Look for the “Weed Warrior” menu tab on the Truckee River 

Watershed Council website.

Do not remove “A” & “B” weeds yourself.

We work with the appropriate county to ensure proper tracking, 

treatment and disposal of these noxious weeds.

Do not report “C” and non-rated weeds. 

Treat “C” rated weeds yourself with the following exceptions. 

Scotch broom, yellow starthistle and yellow toadflax need to be 

reported when found in the Truckee area because they are

recent invaders here. Please use the Bag & Bake method to 

treat the more prevalent invasive weeds on your own property.

Bag & Bake “C” and non-rated weeds.

•	 Dig plants with flowers or seeds, removing as much root 		

as is practical. (See “Management” specific to each weed 

listed in book.)

•	 Double bag seeds and flower parts using strong plastic 	 	

yard waste bags.

•	 Spray plants with dish soap/water solution.

•	 Tie bag and leave out in sun to decompose for at least one 	 	

month.

•	 Dispose of in trash. Do not use “green bags” that are to 	 	

be used for composting and redistribution.

•	 Observe site for regrowth of invasive weeds from 	 	

remaining rootstock and seedlings.
6 7

INDEX COMMON NAME Scientific Name CODE Page INDEX COMMON NAME Scientific Name CODE Page 

THISTLES AND LOOK-ALIKES

 Invasive

BULL THISTLE Cirsium vulgare CIVU 10-11

CANADA THISTLE Cirsium arvense CIAR4 12-13

MUSK THISTLE Carduus nutans CANU4 14-15

SCOTCH THISTLE Onopordum acanthium ONAC 16-17

 Look-alike

ANDERSON’S THISTLE Cirsium andersonii CIAN 18-19

ELK THISTLE Cirsium scariosum CISC2 20-21 

SNOWY THISTLE CIOCC 22-23 

Cirsium occidentale var. candidissimum 

KNAPWEEDS AND LOOK-ALIKES

 Invasive

DIFFUSE KNAPWEED Centaurea diffusa CEDI3 24-25

RUSSIAN KNAPWEED Acroptilon repens ACRE 26-27 

SPOTTED KNAPWEED Centaurea stoebe CEST8 28-29

YELLOW STARTHISTLE Centaurea solstitialis CESO3 30-31

 Look-alike

ASTER Aster spp. 32-33

 Look-alike

BACHELOR’S BUTTONS Centaurea cyanus CECY2 34-35

MUSTARDS AND LOOK-ALIKES

 Invasive

DYER’S WOAD Isatis tinctoria ISTI 36-37

HOARY CRESS Lepidium draba LEDR 38-39

PERENNIAL PEPPERWEED LELA2 40-41

Lepidium latifolium

POISON HEMLOCK Conium maculatum COMA2 42-43

WHITE SWEETCLOVER Melilotus albus MEAL12 44-45

 Look-alike 

YARROW Achillea millefolium ACMI2 46-47

TOADFLAXES AND LOOK-ALIKES

 Invasive

DALMATIAN TOADFLAX Linaria dalmatica LIDA 48-49 

YELLOW TOADFLAX Linaria vulgaris LIVU2 50-51

 Look-alike

SNAPDRAGON Antirrhinum majus ANMA3 52-53

DAISIES AND LOOK-ALIKES

 Invasive

OXEYE DAISY Leucanthemum vulgare LEVU 54-55

 Look-alike

SHASTA DAISY Leucanthemum maximum LEMA8 56-57

BROOMS

 Invasive

SCOTCH BROOM Cytisus scoparius CYSC4 58-59

SPANISH BROOM Spartium junceum SPJU2 60-61

AQUATIC AND LOOK-ALIKES

 Invasive

EURASIAN WATERMILFOIL MYSP 62-63

Myriophyllum spicatum 

 Look-alike 

COMMON ELODEA Elodea canadensis ELCA7 64-65

OTHERS AND LOOK-ALIKES

 Invasive

KLAMATHWEED Hypericum perforatum HYPE 66-67

 Look-alike

SCOULER’S ST. JOHNSWORT HYSC5 68-69

Hypericum scouleri

 Invasive

RUSH SKELETONWEED Chondrilla juncea CHJU 70-71

TEASEL Dipsacus fullonum DIFU2 72-73
8 9

QUICK REFERENCE ID

KNAPWEEDS Bracts Lower Leaves

Diffuse

Knapweed

Russian

Knapweed

Spotted

Knapweed

Yellow

Starthistle

Aster spp.

(look-alike)

Bachelor’s

Buttons

(look-alike)

QUICK REFERENCE ID

THISTLES Flower Head Leaves

Bull Thistle

Canada Thistle

Musk Thistle

Scotch Thistle

Anderson’s

Thistle

(look-alike)

Elk Thistle

(look-alike)

Snowy Thistle 

(look-alike)

vase

drop

disk

oval

cylinder

no stems

rough,

veins

lobed,

spiny

midrib,

hairless

cobweb

hairy

small

flat hairs

long

hairs

spiny combs

papery

spots

spines

no spines,

yellow disk

no spots

deeply

lobed

lobed

deeply

lobed

winged

stem

narrow,

entire

narrow,

entire

reflexed bracts

wooly

hairs
10 11

Also Known As Common thistle

Origin Non-native, invasive

Habitat Meadows, roadsides, disturbed sites

Life Cycle Biennial

Flowering Time Mid-July to fall

Relative Abundance Widespread

Management Dig, removing top 2 inches of root; 

herbicides are available

 Noxious Weed List Nevada-NO; California C-rated

BULL THISTLE Cirsium vulgare CIVU

Plant, Brenneman; Flower, Donaldson

 Height: 1 - 6 ft. 

commonly 2 - 3 ft.

n Stems: spiny and winged

n Leaves: sandpaper texture, 

prominent veins

n Flowers: in clusters at 

ends of branches

n Flower color: pink to purple

Tops of leaves 

rough, sandpaper 

texture

Underside of 

leaf cottony, 

prominently 

raised main vein

Rosette leaves

rough, prominent veins

1 - 1.5 in.

Flower head

vase-shaped

Non-native Invasive
12 13

Also Known As Field thistle

Origin Non-native, invasive

Habitat Roadsides, rangelands, forests, lawns,

gardens, moist and disturbed sites

Life Cycle Perennial

Flowering Time Mid-July to fall

Relative Abundance Infrequent

Management Aggressive; pulling and burning favor 

root resprouting; use chemical 

control for several years 

 Noxious Weed List Nevada C-rated; California B-rated

CANADA THISTLE Cirsium arvense CIAR4

Donaldson

 Height: 1.5 - 4 ft. 

commonly 2 - 3 ft.

n Stems: smooth and ridged 

with no spines

n Leaves: smooth and 

sessile

n Flowers: multiple 

small flower heads in 

clusters on each stem

n Flower color:

light purple to white

Flower head

drop-shaped

Bracts small 

and flat against 

head, tips weak

0.5 in.

Leaves

deeply lobed

Non-native Invasive
14 15

Also Known As Nodding thistle 

Origin Non-native, invasive

Habitat Pastures, forest, rangelands,

roadsides, waste areas, ditches

Life Cycle Biennial

Flowering Time Mid-July to fall

Relative Abundance Infrequent

Management Dig, removing top 2 inches of root; 

herbicides are available

Noxious Weed List Nevada B-rated; California A-rated

MUSK THISTLE Carduus nutans CANU4

Plant, Miller; Flower, Donaldson

 Height: 1 - 6 ft.

commonly 3 - 4 ft.

n Stems: spiny and winged

n Leaves: hairless, prominent 

light-green midrib

n Flowers: single, very large 

flower at end of bent, 

naked stem

n Flower color: deep pink

to purple

Flower head

disk-shaped

2 - 3.5 in.

Bracts large and spiny; 

purplish in color

Light-green 

midrib

Non-native Invasive

Rosette leaves hairless, 

light-green midrib, 

whitish margins
16 17

Also Known As Winged thistle

Origin Non-native, invasive

Habitat Waste areas, roadsides, disturbed soils

Life Cycle Biennial; rarely annual

Flowering Time Mid-July to fall

Relative Abundance Infrequent

Management Dig, removing top 2 inches of root; 

herbicides are available

Noxious Weed List Nevada B-rated; California A-rated

SCOTCH THISTLE Onopordum acanthium ONACDonaldson

 Height: up to 10 ft. 

commonly 5+ ft.

(the tallest of the thistles)

 Stems: spiny, 

prominently winged

 Leaves: hairy and sessile

 Flowers: in groups of 2 or 3 

on branched tips

 Flower color: purple

Leaves hairy, 

giving a grayish 

appearance

Many spiny, 

needle-like bracts

1-2 in.

Flower head

flattened globe

Stems spiny

and winged

Non-native Invasive
18 19

Also Known As Rose thistle

Origin Native

Habitat Open places, woodlands, forests

Life Cycle Biennial

Flowering Time July to fall

Relative Abundance Widespread

Management Desirable native plant; do not disturb

Noxious Weed List Nevada-NO; California-NO

ANDERSON’S THISTLE Cirsium andersonii CIANBrenneman

 Height: 2 - 4 ft.

n Stems: purplish and 

thornless

n Leaves: divided and wavy 

with spiny margin

n Flowers: single

flower at end of stem 

n Flower color: rose red to 

reddish purple

Flower head

cylinder-shaped

Rosette leaves not 

prominently veined, 

small flat hairs 

Leaf margins

wavy and spiny

0.75 - 1.5 in.

Native Look-alike
20 21

Also Known As Drummond’s thistle

Origin Native

Habitat Moist places at mid to high elevations

Life Cycle Biennial

Flowering Time June to August

Relative Abundance Moderate

Management Desirable native plant; do not disturb

Noxious Weed List Nevada-NO; California-NO

ELK THISTLE Cirsium scariosum CISC2

Brenneman

Stemless flower

 Height: up to 3 ft. 

generally less than 1 ft.

n Stems: usually no stems; 

forms round flat rosette

n Leaves: lobed, somewhat 

spiny, pale green foliage

n Flowers: extend directly 

from rosette

n Flower color: white

to pale lavender

Native Look-alike

Rosette leaves have

long golden hairs; long 

fine spines at leaf margins
Native Look-alike

22 23

Also Known As None

Origin Native

Habitat Disturbed areas, shrubby areas, 

open woodlands

Life Cycle Biennial

Flowering Time July to September

Relative Abundance Widespread in Northern California

Management Desirable native plant; do not disturb

Noxious Weed List Nevada-NO; California NO

SNOWY THISTLE 

Plant, Urie; Flower, Monroe Calphotos

Cirsium occidentale

var. candidissimum CIOCC

 Height: 1.5 to 6.5 ft. 

n Stems: densely 

white wooly hairs

n Leaves: densely white 

wooly hairs on both 

surfaces

n Flowers: single or in 

clusters at the end of 

branches

n Flower color: pink to red

Densely white

wooly hairs

Large 

reflexed bracts,

wooly hairs

3/4 - 2 in.
24 25

Also Known As Tumble knapweed

Origin Non-native, invasive

Habitat Roadsides, waste areas, dry 

rangelands, disturbed sites

Life Cycle Annual to short-lived perennial

Flowering Time June to August

Relative Abundance Infrequent

Management Minimize seed production; pull or dig

plants several times per year and 

monitor for several years;

herbicides are available

Noxious Weed List Nevada B-rated; California A-rated

DIFFUSE KNAPWEED Centaurea diffusa CEDI3 Donaldson

Bract tips

spiny; margins 

divided like

teeth of comb

 Height: 1 - 2.5 ft.

n Stems: rough to touch

n Leaves: upper, entire;

lower, deeply lobed

n Growth form: maintains 

bush shape; after frost,

can break off and tumble

n Flower color: white to

pale pink

Stems stiff and 

widely branching

Lower leaves 

deeply lobed

Upper leaves 

narrow and

entire

Non-native Invasive
26 27

Also Known As Creeping knapweed

Origin Non-native, invasive

Habitat Roadsides, riverbanks, ditches, 

pastures, waste places

Life Cycle Rhizomatous perennial

Flowering Time July to fall

Relative Abundance Infrequent

Management Cut or mow prior to seed set to reduce 

current year’s growth; chemical control 

is needed

Noxious Weed List Nevada B-rated; California B-rated

RUSSIAN KNAPWEED Acroptilon repens ACREDonaldson

Bract margins 

papery,

NOT spiny

 Height: 1 - 3 ft. 

generally 2 - 3 ft.

n Stems: erect, cobwebby

n Leaves: upper, entire; 

lower and rosette, lobed

n Growth form: thick 

rounded clumps with 

drooping branches

n Root: black below crown

n Flower color: pink to purple 

Upper leaves 

narrow and

entire

Lower leaves

lobed

Stems openly 

branched

Non-native Invasive
28 29

Also Known As Centaurea maculosa

Origin Non-native, invasive

Habitat Disturbed soil, rangelands, pastures, 

meadows, roadsides, areas with 

summer rainfall

Life Cycle Perennial; sometimes biennial

Flowering Time July to early September

Relative Abundance Moderate

Management Minimize seed production by cutting or 

mowing; dig, removing top 2 - 6 inches

of root; herbicides are available

Noxious Weed List Nevada A-rated; California A-rated

SPOTTED KNAPWEED Centaurea stoebe CEST8

Plant, Breckenridge CDFA; Flower, Donaldson

Bract tips dark, 

finely fringed, 

spineless

 Height: 1 - 5 ft. 

generally closer to 3 ft.

n Stems: erect and rough

n Leaves: upper, linear; 

lower, divided

n Growth form: tall with 

open branching

n Flower color: pink to purple

Upper leaves

narrow and entire

Lower leaves 

deeply lobed 

and smooth

Note leaf 

placement

Stems openly 

branched

Non-native Invasive
30 31

Also Known As None

Origin Non-native, invasive

Habitat Roadsides, waste areas, grasslands

Life Cycle Annual

Flowering Time Late June to September

Relative Abundance Widespread (infrequent in Truckee 

River watershed)

Management Pull, dig or mow at first sign of yellow 

flowers; herbicides are available

Noxious Weed List Nevada A-rated; California C-rated

YELLOW STARTHISTLE Centaurea solstitialis CESO3Donaldson

Lower leaves 

deeply lobed

 Height: 0.5 - 5 ft. 

commonly 2 ft.

n Stems: winged

n Leaves: gray and hairy; 

upper, entire;

lower, deeply lobed

n Growth form: stiffly 

branching

n Flower color: yellow

Upper leaves 

entire

Non-native Invasive

Long spines at 

tips of bracts

(up to 1 in. long)
32 33

Also Known As Various

Origin Native

Habitat Meadows, gardens 

Life Cycle Annual or perennial

Flowering Time Late July to fall

Relative Abundance Widespread

Management Desirable native plant; do not disturb

Noxious Weed List Nevada-NO; California-NO

ASTER Aster spp. ASTER

Donaldson

Bracts do not 

have spines

Leaves

narrow and entire

 Height: variable,

often 1 - 2 ft.

n Stems: smooth to hairy

n Leaves: upper and lower 

leaves narrow and entire

n Growth form: ranges from 

short to tall

n Flower color: variable, 

often pink to purple with 

yellow center

Native Look-alike
34 35

Also Known As Cornflower

Origin Non-native, can be invasive,

has escaped from cultivation

Habitat Disturbed grasslands, open woods,

ornamental plantings

Life Cycle Annual

Flowering Time July to September

Relative Abundance Widespread

Management Mechanical controls (pull, dig, hoe); 

herbicides are available

Noxious Weed List Nevada-NO; California-NO

BACHELOR’S BUTTONS Centaurea cyanus CECY2Donaldson

 Height: up to 3 ft.

n Stems: erect and branching

n Leaves: grayish and hairy;

upper and lower leaves 

narrow and entire

n Growth form: tall, bushy

n Flower color: multicolored 

(white, blue, purple,

pink, red)

Non-native Look-alike

Leaves narrow and 

entire; generally 

not toothed except 

lower leaves

Bract tips 

pale, finely 

fringed, 

spineless
 

36 37

Also Known As Marlahan mustard

Origin Non-native, invasive

Habitat Meadows, roadsides, 

streambanks, rangelands 

Life Cycle Biennial to short lived perennial 

Flowering Time June to July

Relative Abundance Infrequent

Management Dig, removing top 2 inches of root;

observe site yearly to look for sprouting 

rosettes; herbicides are available

Noxious Weed List Nevada A-rated; California B-rated

DYER’S WOAD Isatis tinctoria ISTI

Plant, Welch; Flower, Belsher-Howe

	Height: up to 4 ft. 

n Stems: single stem gives 

rise to multiple branches 

with multiple flower clusters

n Leaves: blue-green foliage 

with cream-colored midrib;

upper leaves clasp stem, 

arrowhead-shaped;

lower leaves petiolate

n Flower color: yellow

Rosette leaves 

oblanceolate with

weakly rounded tips

Fruits black 

to dark purple; 

hang like pendants 

from stem

Long 

petiole on

rosette leaves

Tiny 4-petaled 

flowers in dense 

clusters near 

ends of branches

Non-native Invasive

Lobes 

clasp stem 

on upper 

leaves
 

38 39

Also Known As Whitetop, short whitetop,

 Cardaria pubescens

Origin Non-native, invasive

Habitat Meadows, fields, roadsides, ditches,

streambanks, rangelands 

Life Cycle Rhizomatous perennial

Flowering Time May to June

Relative Abundance Infrequent

Management Mow two to three times per year at 

bud stage to slow spread; do not pull,

as plants will grow from root fragments;

chemical control is needed

Noxious Weed List Nevada C-rated; California B-rated

HOARY CRESS Lepidium draba LEDR

Donaldson

 Height: up to 2 ft. 

commonly 1 ft.

n Stems: many stems give

rise to multiple branches 

with one flower cluster

n Leaves: blue-green foliage;

upper leaves clasp stem; 

lower leaves petiolate

n Seed Shape: round

n Flower color: white

2 lobes 

clasp stem on 

upper leaves

Leaves

lance-shaped

One branch

Tiny 4-petaled 

flowers in dense 

clusters near 

ends of branches

Non-native Invasive
40 41

Also Known As Tall whitetop

Origin Non-native, invasive

Habitat Riparian areas, floodplains, meadows, 

seasonally wet areas, roadsides

Life Cycle Rhizomatous perennial

Flowering Time Late June to August

Relative Abundance Moderate

Management Do not pull, dig, or cut the roots,

as this may stimulate new growth; 

chemical control is needed

Noxious Weed List Nevada C-rated; California B-rated

PERENNIAL PEPPERWEED Lepidium latifolium LELA2Donaldson

Tiny 4-petaled 

flowers in dense 

clusters near ends 

of branches

 Height: 1 - 6 ft.

commonly 3+ ft.

 Stems: each stem gives 

rise to multiple branches 

with multiple flower clusters

 Leaves: upper leaves, sessile; 

lower leaves, petiolate; 

basal leaves, much larger 

than upper leaves

n Seed Shape: round

n Flower color: white

Multiple 

branches 

Stems branch 

from juncture 

of leaf with 

main stem

Leaves lance-shaped; 

leaf margins

smooth or toothed

Non-native Invasive
42 43

Also Known As Poison parsley

Extremely poisonous if ingested

Origin Non-native, invasive

Habitat Wet areas in meadows, seeps, springs 

and floodplains

Life Cycle Biennial

Flowering Time July to Fall

Management Multiple mowing in bud stage 

or chemical control

Noxious Weed List Nevada C-rated; California-NO

POISON HEMLOCK Conium maculatum L. COMA2

Urie

 Height: 3 - 8 ft.

commonly 3+ ft.

 Stems: branched, light 

green with purple spots

 Leaves: compound, 

lacy resembling parsley, 

seedlings may appear 

fern-like

n Flower color: white

Stems light 

green with 

purple spots

Non-native Invasive

Secondary

Umbel Umbel

Secondary

Umbel

Leaves

fern-like
44 45

Also Known As None

Origin Non-native, used in soil

stabilization mixes

Habitat Roadsides, waste areas

Life Cycle Annual to biennial

Flowering Time June to August

Relative Abundance Widespread

Management Hand pull wearing gloves; dig or mow 

prior to seed set; herbicides available

Noxious Weed List Nevada-NO; California-NO

WHITE SWEETCLOVER Melilotus albus MEAL12Brenneman

Pea-shaped 

flowers

 Height: 2 - 6 ft.

commonly about 3 - 5 ft.

n Stems: well-branched and 

coarse

n Leaves: 3 leaflets

n Flower color: white

Leaves consist 

of 3 leaflets,

margins finely 

toothed

Many small 

fragrant flowers 

borne on 

irregular spikes 

at the ends 

of elongated 

stems 

Non-native Invasive
46 47

Also Known As Common yarrow, milfoil

Origin Native and introduced, can be invasive

Habitat Gardens, meadows, grasslands, forests

Life Cycle Perennial

Flowering Time June to September

Relative Abundance Widespread

Management Dig, removing as much root as 

possible; forms dense mat if mowed;

chemical control is available

Noxious Weed List Nevada-NO; California-NO

YARROW Achillea millefolium ACMI2

Plant, Brenneman; Flower, Donaldson

Flower heads 

flattened,

dome-shaped 

corymbs

 Height: 2 - 3 ft.

n Stems: hairy-wooly

n Leaves: feather-like; evenly 

distributed along stem; 

lower leaves larger

n Flower color: white or pink

Leaves hairy and 

very finely pinnately 

divided, appearing 

feather-like

Native Look-alike
48 49

Also Known As Wild snapdragon,

 Linaria genistifolia ssp. dalmatica

Origin Non-native, invasive

Habitat Roadsides, pastures, rangelands, 

cultivated fields

Life Cycle Perennial

Flowering Time July to fall

Relative Abundance Moderate

Management Pull or dig for several years, removing

as much root as possible; do not mow; 

chemical control is available

Noxious Weed List Nevada A-rated; California A-rated

DALMATIAN TOADFLAX Linaria dalmatica LIDADonaldson

 Height: up to 3 ft.

 Stems: erect and branched

 Leaves: ovate, alternate 

and entire; succulent and 

waxy

 Growth form: more 

scattered than yellow 

toadflax

 Flower color: yellow, with 

orange, bearded throat

Non-native Invasive

Flowers borne 

in axils of upper 

leaves and bracts

Spurs long, 

somewhat 

curved or 

straight

Leaves ovate, 

tips pointed

Leaves

clasp stem
50 51

Also Known As Butter and eggs

Origin Non-native, invasive

Habitat Rangelands, roadsides, waste places, 

cultivated fields

Life Cycle Perennial

Flowering Time July to fall

Relative Abundance Moderate (infrequent in Truckee 

River watershed)

Management Pull or dig for several years, removing 

as much root as possible; do not mow; 

chemical control is available

Noxious Weed List Nevada A-rated; California-NO

YELLOW TOADFLAX Linaria vulgaris LIVU2

Plant, Brenneman; Flower, Charles Webber © CA Academyof Sciences

 Height: 1 - 2 ft.

shorter than dalmatian 

toadflax

 Leaves: linear, smooth to 

sparsely hairy; succulent 

and waxy

 Growth form: tends to 

grow in crowded patches

 Flower color: yellow, with 

orange, bearded throat

Non-native Invasive

Leaves alternate, 

crowded close together

Leaves linear, 

pointed at both ends 

Spur 
52 53

Also Known As None

Origin Non-native

Habitat Ornamental gardens

Life Cycle Annual to perennial

Flowering Time June to fall

Relative Abundance Widespread

Management None; recommended garden flower

Noxious Weed List Nevada-NO; California-NO

SNAPDRAGON Antirrhinum majus ANMA3

Plant, Brenneman; Flower, Donaldson

Flowers in 

terminal racemes

 Height: 0.5 - 3 ft. 

n Leaves: upper, long and 

narrow; lower, lanceolate;

soft, not waxy

n Flowers: fuzzy-hairy

n Flower color: yellow, but 

other colors are available

No spur

Upper leaves 

long and narrow

Lower leaves 

lanceolate

Non-native Look-alike
54 55

Also Known As White daisy

Origin Non-native, invasive

Habitat Meadows, roadsides, waste places, 

gardens

Life Cycle Perennial

Flowering Time June to August

Relative Abundance Widespread

Management Pull or dig before seed production; 

herbicides are available

Noxious Weed List Nevada-NO; California-NO

OXEYE DAISY Leucanthemum vulgare LEVU

Donaldson

Lower leaves 

lobed or toothed

 Height: 0.8 - 2 ft.

n Stems: smooth to

slightly hairy

n Leaves: upper, toothed

and sessile; lower, 

pinnately lobed or toothed

n Flowers: single flower 

heads grow at ends

of branches; bracts are 

lined in black

n Flower color: white

with yellow center

Rosette leaves

spatulate; margins

crenulate

Approximate disk flower

to ray flower ratio

Upper leaves 

toothed, sessile; 

smaller towards

top of stem

Leaves

spoon-shaped

Non-native Invasive
56 57

Also Known As None

Origin Non-native, naturalized

Habitat Well-drained soil, full sun,

ornamental gardens

Life Cycle Perennial

Flowering Time July to September

Relative Abundance Widespread

Management None; recommended garden flower

Noxious Weed List Nevada-NO; California-NO

SHASTA DAISY Leucanthemum maximum LEMA8

Plant, Brenneman; Flower, Donaldson

 Height: 1 - 3 ft. taller than oxeye daisy

n Stems: stiff,

more-or-less smooth

n Leaves: upper, serrate and

sessile; lower, petiolate

n Flowers: single flower 

heads grow at ends 

of branches; heads

larger than oxeye daisy

n Flower color: white 

with yellow center 

Rosette leaves oval; 

margins serrate

Approximate disk flower

to ray flower ratio

Upper leaves 

serrate and sessile; 

smaller toward top 

of stem

Non-native Look-alike
58 59

Also Known As Common broom, English broom 

Origin Non-native, invasive

Habitat Pastures, forests, waste areas

Life Cycle Long lived perennial

Flowering Time May to July

Relative Abundance Moderate (infrequent in Truckee 

River watershed)

Management Pull with heavy-duty weed wrench 

removing as much root as possible: 

observe site yearly and pull seedlings; 

chemical control most effective treatment

Noxious Weed List Nevada-NO; California C-rated

SCOTCH BROOM Cytisus scoparius CYSC4

Plant, VanZuuk; Flower, Keir Morse

Non-native Invasive

Numerous showy 

pea flowers 

Seed pods flattened, 

only margins hairy 

 Height: woody shrub

up to 8 ft.

n Stems: 5-angled; 

star-shaped cross-section 

n Branches: dark green;

more-or-less erect

n Leaves: 3 leaflets, 

sometimes simple on 

new twigs, deciduous

n Flower color: deep yellow; 

slight to no fragrance

3 leaflets,

sometimes simple

Flowers single

or paired in 

leaf axils

Stems 

sharply

5-angled
60 61

Also Known As Weaver’s broom

Origin Non-native, invasive

Habitat Roadsides, forests and rangelands 

Life Cycle Long lived perennial

Flowering Time May to July

Relative Abundance Moderate (infrequent in Truckee 

River watershed)

Management Pull with heavy-duty weed wrench 

removing as much root as possible:

observe site yearly and pull seedlings; 

chemical control most effective treatment

Noxious Weed List Nevada-NO; California C-rated

SPANISH BROOM Spartium junceum SPJU2

Donaldson

Non-native Invasive

Flowers in 

open racemes 

at stem tips

Stems finely 

ribbed, round in

cross-section

 Height: woody shrub 

up to 8 ft. 

n Stems: smooth or finely 

ribbed; round cross-section

n Branches: dark green;

more-or-less erect

 Leaves: simple, entire; 

sparse and deciduous

n Flower color: yellow; 

strong fragrance

Seed pods 

slightly flattened, 

densely covered 

with long hairs

Leaves 

simple

Numerous showy 

pea flowers 
62 63

Also Known As Spike watermilfoil

Origin Non-native, invasive

Habitat Ponds, ditches, streams, lakes

Life Cycle Perennial

Flowering Time June through September

Management Hand removal, taking care to avoid 

releasing fragments

Noxious Weed List Nevada-YES; California-NO

EURASIAN WATERMILFOIL

Habit, Sasaki; Close-up, DiTomaso Calphotos

Myriophyllum

spicatum MYSP

Leaves collapse 

when out of water 

Native stiffer, does 

not collapse

Leaves arranged in 

whorls of 4 around 

stem at each node

n Growth form: submersed 

aquatic; forms mats; 

spreads by plant fragments

n Stems: branch near 

water’s surface; growing 

stems and tips are red

n Leaves: feather-like; dark 

green to brown

n Flowers: tiny and stand 

above the water surface

n Flower color: pinkish;

spike inflorescence

14+ leaflet pairs per leaf

Native 5-12 leaflet pairs

Non-native Invasive
64 65

Also Known As American waterweed,

Canadian waterweed

Origin Native

Habitat Ponds, ditches, streams, lakes, reservoirs

Life Cycle Perennial

Flowering Time Summer 

Management Usually not a problem, remove by hand

when it becomes dominant or problematic

Noxious Weed List Nevada-NO; California-NO

COMMON ELODEA Elodea canadensis ELCA7

Habit, Miller; Close-up, Landry Calphotos

 Growth form: submersed 

aquatic; spreads by plant 

fragments and turions

n Stems: branch at nodes

n Leaves: dark green, 

most often in whorls of 3; 

lanceolate to oblong 

n Flower color: white; 

flowers bloom at the water 

surface; have 3 small petals

Leaves arranged

in whorls of 3

Native Look-alike

Leaves do not 

collapse when 

out of water. 
66 67

Also Known As St. John’s Wort

Origin Non-native, invasive

Habitat Pastures, meadows, roadsides,

waste areas

Life Cycle Perennial

Flowering Time June to late September

Relative Abundance Moderate

Management Pull or dig repeatedly; use biocontrol 

insects; chemicals are available

Noxious Weed List Nevada A-rated; California C-rated

KLAMATHWEED Hypericum perforatum HYPE Brenneman

5 separate 

petals

 Height: 1 - 3+ ft. 

n Stems: erect with numerous 

rust-colored branches

n Leaves: elliptic to oblong, 

entire, opposite, sessile; 

not over 1 in. long

n Growth form: bushy

n Branches: somewhat

2-ridged and woody at

the base

n Flower color: yellow

Non-native Invasive

Occasional tiny 

black dots at 

edges of petals 

Older flower 

petals twist

1 in.

Flat-topped 

cymes

Transparent dots

on leaves

More flowers 

per stem

than native
68 69

Also Known As None

Origin Native

Habitat Streambanks, meadows

Life Cycle Tap-rooted perennial

Flowering Time Summer 

Relative Abundance Moderate

Management Desirable native plant; do not disturb

Noxious Weed List Nevada-NO; California-NO

SCOULER’S ST. JOHNSWORT Hypericum

scouleri HYSC5Plant, Eliassen Calphotos ; Flower, Matson Calphotos

5 separate 

petals

Fewer

flowers per 

stem than 

invasive

 Height: 0.5 - 2.5 ft.

n Stems: slender; extend

from base

n Leaves: ovate to oblong, 

flat, more or less clasping

n Growth form: upright 

and stemmy

n Flower color: yellow

Native Look-Alike

Tiny black dots at 

edges of petals 

1 in.

Leaf margins

black-dotted, lower surface

inconspicuously dotted
70 71

Also Known As Skeleton weed

Origin Non-native, invasive

Habitat Roadsides, rangelands, pastures, 

disturbed soils 

Life Cycle Perennial with extensive, deep root 

system

Flowering Time Mid-July through frost

Relative Abundance Infrequent

Management Difficult to control without herbicides 

due to extensive deep root system

Noxious Weed List Nevada A-rated; California A-rated

RUSH SKELETONWEED Chondrilla juncea CHJUDiTomaso

 Height: 1 - 4 ft.

n Stems: rigid and wiry; 

highly branched; cut 

surfaces exude milky sap 

n Leaves: upper, narrow

and entire, inconspicuous; 

stems often lack leaves

n Growth form: bushy

n Flower color: yellow

Non-native Invasive

Rosette leaves 

sharply toothed

Lower 4 - 6 inches of 

stem has downwardly 

bent coarse hairs

Stems

smooth 

above
72 73

Also Known As Common teasel, wild teasel

Origin Non-native, invasive

Habitat Irrigation ditches, canals, wetlands,

riparian areas, disturbed sites

Life Cycle Tap-rooted biennial

Flowering Time July to fall

Relative Abundance Infrequent

Management Dig or hand-pull, removing as much root 

as possible; herbicides are available

Noxious Weed List Nevada-NO; California-NO 

TEASEL Dipsacus fullonum DIFU2

DiTomaso

Ridges lined 

with stiff prickles

Stiff prickles

on lower midrib

 Height: up to 7 ft. 

commonly 3+ ft.

n Stems: branched,

rough and spiny

n Leaves: conspicuously 

veined; stem leaves

lanceolate, up to 10 in.

n Growth form: erect

n Flower color: lavender to 

purple, rarely white

Non-native Invasive

Leaves paired,

fused at base 

around stem

Flowers in dense

egg-like heads with 

large, spine-like bracts
74 75

GLOSSARY

Alternate: Borne singly and changing sides at each node, 

such as leaves. 

Axil: The angle formed between the stem and any part, 

such as a leaf, attached to it.

Bract: A modified leaf at the base of a flower.

Corymb: A flat-topped or round-topped arrangement of 

flowers where the lower flower stalks are longer than the 

upper stalks.

Cyme: A flat-topped or round-topped arrangement of 

flowers in which the terminal flower blooms first.

Crenulate: Having very small, rounded teeth on the leaf 

margin.

Disk flower: The tiny, tubular flower of the Asteraceae 

that forms the center disk of the flowerhead.

Divided: Deeply lobed leaf in which lobes are indented to 

the base or the midrib.

Elliptic: Shaped like an ellipse or a narrow oval, broadest 

in the middle.

Entire: The margins are smooth, without teeth or lobes.

Inflorescence: A flower cluster.

Linear: Narrow and flat with sides or edges parallel, as 

in a leaf.

 

Lobed: Bearing lobes cut less than halfway to base or midvein.

Margin: The outer edge of the leaf, which may be 

smooth, serrated, lobed, etc.

Midrib: The middle vein of a leaf.

Oblanceolate: Leaf shape in which the length is at least 

3x longer than wide, but broadest above middle.

Oblong: Leaf shape in which the leaf is two to four times 

longer than it is wide, with nearly parallel sides.

Opposite: Leaves or other structures borne across from 

each other at the same node.

GLOSSARY

Ovate Leaf: Egg-shaped leaf that is attached at the broad end.

Palmate: Having three or more veins or lobes radiating 

from a central point, similar to the fingers on a hand.

Panicle: A branched inflorescence in which the flowers 

bloom from the bottom up.

Petiole: The stalk of a leaf.

Pinnate: A compound leaf with leaflets arranged on 

opposite sides of the axis.

 

Raceme: A simple, elongated arrangement of flowers.

Ray flower: The long, narrow flower that radiates 

outward from the disk flower in the Asteraceae family.

Each ray flower resembles a single petal.

Rhizomatous: Having rhizomes, or horizontal underground 

stems that produce shoots above and roots below.

Rosette: A dense, basal cluster of leaves arranged in a 

circular fashion around one point, usually at ground level.

Serrate: With sharp teeth directed forward; generally 

refers to leaf edges.

Sessile: Without a stalk of any kind; for example, a leaf 

directly attached to a stem.

Spatulate: Shaped like a spatula, with a rounded blade 

that tapers to the base.

Spike: An unbranched, long flower stalk in which the 

flowers attach directly to the stem and mature from the 

bottom upwards.

Toothed: Having sharp points or lobes along a margin, as 

on a leaf.

Turion: Detached winter bud by means of which many 

water plants survive winter. 

Umbel: A flat-topped flower arrangement.

Winged stem: A stem with one or more thin, flat 

margins protruding along the length of the stem. 
76 77

CONTACT INFORMATION

For weed information and mapping on the 

Tahoe National Forest, contact:

Tahoe National Forest, East Zone Botanist

(530) 587-3558 surie@fs.fed.us

Non-native Invasive Plant Coordinator

(530) 478-6243 kvanzuuk@fs.fed.us

For weed control information on private land contact:

Nevada County Agriculture Department

(530) 273-2648

Placer County Agriculture Department 

(530) 889-7372

Plumas-Sierra County Agriculture Department

(530) 283-6365

Natural Resources Conservation Service

(530) 283-7510

Truckee River Watershed Council

(530) 550-8760 jhalderman@truckeeriverwc.org

Funded by: 

WEED MAPPING

Your Help Is Needed For Weed Mapping!

Regular mapping and inventory helps determine which 

species are present, what management methods are 

appropriate, and whether management has been a success.

Within the Truckee River watershed, if you find potential 

non-native invasive plants, please refer to the website – 

www.truckeeriverwc.org – “Report A Weed”. Submit “A 

and “B” rated non-native invasive plants or the “C” rated 

Scotch broom, yellow starthistle or yellow toadflax via the 

website. Do not report widespread “C” rated non-native 

invasive plants.

Please include the following information:

•	 Name, e-mail and contact information

• 	The weed you are reporting (look at the identification

flower pictures on website)

•	 Estimated number of weeds found within infestation

•	 Geographic location by using one of three available

methods. You may enter the street address, GPS 

coordinates in NAD 83, or use the satellite map or 

regular map on the website to place a marker

• 	Size of the infestation in square feet or acres

Please do not take any management actions or remove plants 

until they have been positively identified. Consult the website 

for identification tools while reporting to the website.

Outside the Truckee River watershed on private property,

contact the appropriate county Agricultural Department or 

see page 77 for contact information.

On-going Programs 

The Nevada Placer Weed Management Area in conjunction 

with the Tahoe National Forest have been mapping weeds 

in the Truckee River watershed since 2001 in Sierra, Placer, 

and Nevada Counties. The Plumas-Sierra Noxious Weed 

Management Group has been mapping weeds in Sierra and 

Plumas Counties since 2000.