Selected 

Invasive 

Plants

of Alaska

2007

United States

Department of 

Agriculture

Forest Service

Alaska Region

R10-TP-130B
On the cover: Bull Thistle

photo taken by Michael Rasy, UAF Cooperative Extension Service 

Bull thistle forms dense, spiny, stands in meadows, pastures, streamsides, 

and forest openings. This highly-competitive weed monopolizes water, 

nutrients, and growing space. Once established, stands of bull thistle can 

suppress the growth of conifer seedlings, reduce land values, and restrict 

the movement of people and animals.
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ III

When trying to identify an unknown plant, color photos often help. 

This pocket guide provides a selection of invasive plants found across 

Alaska today. This booklet is not intended to take the place of more 

comprehensive reference guides, but to help those unfamiliar with these 

species to begin to recognize them, as the first step towards taking action.

In recent years, well established and expanding 

populations of highly invasive plants have been 

documented in Alaska.

These species pose a serious threat to Alaska's 

agriculture, tourism, wildlife, fisheries, and 

subsistence resources.

Alaska is in an unique position to avoid the 

extensive invasive plant problems that plague the 

rest of the U.S.
Invasive plants in Alaska: Addressing this situation NOW will yield 

benefits for years to come.

Most introduced plant species are beneficial to Alaskans. We enjoy them in our 

gardens and they are agricultural staples.

However, a small subset of introduced plants is “invasive.” These non-native 

plants aggressively spread into places where they are not wanted.

People and vehicles generally spread invasive plants from human habitation 

centers outwards along transportation routes (roads, airports and float ponds, 

trails and rivers) as they move materials and goods.

Thank you for doing your part to insure that these invasive plant species, and 

others like them, do not spread into Alaska's wildlands.

This document was produced by:

Michael Shephard, USDA Forest Service, State & Private Forestry

Tom Huette, USDA Forest Service, State & Private Forestry

Jamie M. Nielsen, UAF Cooperative Extension Service

Charles Lindemuth, Chugach Design Group

Photos provided by the USDA Forest Service State & Private Forestry

or the UAF Cooperative Extension Service, unless otherwise noted.

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OFTHE)NTERIOR
Community members pull together to 

control purple loosestrife in a city park.

Japanese knotweed taking over a 

thimbleberry patch at the base of a 

totem pole in Juneau
In Alaska we are concentrating on prevention,

early detection, and rapid response.

Prevention:

Keeping these invasive plant species from becoming established in 

Alaska is the highest priority. This booklet is a tool to help identify 

some of the invasive plant species of greatest concern in Alaska.

Early Detection & Rapid Response:

Not only is it important to recognize these plants, but it is imperative 

that we find small infestations before they become too difficult to 

control.

The Alaska Soil and Water Conservation Districts, and many partner 

organizations, are in the process of forming “Cooperative Weed 

Management Areas” (CWMAs) across the state, to detect, monitor and 

treat invasive plant populations.
For additional information about invasive plants in Alaska: 

Contact your local UAF Cooperative Extension Service office or 

appropriate local land management agency.

Or visit:

http://akipm.net

www.fs.fed.us/r10/spf/fhp/

www.cnipm.org/index.html

To view or contribute to the state-wide database of exotic plants and 

see the ranking of invasive plants in Alaska:

akweeds.uaa.alaska.edu

(see back pages for index)
Canada Thistle (Cirsium arvense) Sunflower Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/

Canada Thistle (Cirsium arvense) Sunflower Family

• A perennial that grows to five feet tall with erect, ridged, 

branching stems. Leaves curled, wavy, oblong, alternate on 

stem with woolly hairs on underside. Leaves arise directly from 

the stem without a distinct leaf stalk. Flowers are purple-pink 

in clusters at the ends of branches.

• Forms colonies via an extensive horizontal and vertical root 

system; can eventually cover acres. Also spreads by windblown seeds. Young plants appear as basal rosettes that bolt 

in late summer. Grows in fields, pastures, forests, and along 

roadsides, ditches, and river banks.

• Restricts recreational land use, scratches and infects 

animal skin, and produces allelopathic chemicals to 

suppress surrounding vegetation. Very difficult to 

eradicate once established.
Bull Thistle (Cirsium vulgare) Sunflower Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/

Bull Thistle (Cirsium vulgare) Sunflower Family 

• Biennial erect plant rises from a fleshy taproot. A large, flat 

rosette forms in the first year, and flowers and stems elongate 

in the second year. Stem grows 2 to 5 feet tall with many 

spreading branches. Leaves hairy and prickly on upper side, 

and cottony underneath. Stems have irregular spiny “wings.” 

Flower heads are 1.5 to 2 inches, urn shaped, purple ray 

florets. Bracts under flowers are fleshy and tipped with spines.

• Found on disturbed sites, roadsides, and riparian areas. Found 

in Anchorage and Southeast Alaska.

• Restricts recreational land use, decreases land value, and 

competes with native vegetation for water, space, and 

light.
Oxeye Daisy (Leucanthemum vulgare) Sunflower Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 

Oxeye Daisy (Leucanthemum vulgare) Sunflower Family

• A short-lived showy perennial that spreads vegetatively 

by rhizomes or from seeds. Heads solitary at the ends of 

branches, consisting of ray and disc flowers. White ray florets 

0.5 to 1 inch long. Yellow discs 0.5 to 1 inch across. Leaves 

hairless to sparsely hairy, alternate along the stem, becoming 

progressively smaller towards the top, oblanceolate, with 

crenate to lobed margins. Upper leaves toothed, lacking a 

petiole.

• Common on roadsides, disturbed areas, beach meadows, and 

landscaped areas. Frequently a component of wildflower seed 

mixes.

• Forms dense colonies, is unpalatable to grazing animals 

and insects, and hosts several plant viruses. Heavy 

infestations can cause soil erosion.
Spotted Knapweed (Centaurea biebersteinii) Sunflower Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/

Spotted Knapweed (Centaurea biebersteinii) Sunflower 

(or C. stoebe L.) Family

• Biennial or short-lived perennial. Plants grow to three feet tall 

from a stout taproot. Basal rosettes have deeply lobed graygreen leaves. Flower heads solitary at the ends of branches. 

Involucral bracts beneath flowers are stiff and topped with dark 

comb-like fringe giving a spotted appearance. Flower heads 

pink-purple, consisting of ray florets only, solitary at the end of 

stem branches.

• Spreads only by seeds. Adapted to well-drained soils. Seeds 

dispersed near the parent plant or transported by people, 

wildlife, vehicles, and in soil, crop seed, and contaminated 

hay. Look for this plant along roadsides in Alaska. Found in 

Anchorage, Valdez, and numerous locations in Southest Alaska.

• Responsible for millions of dollars in economic loss and 

environmental damage in the western United States.
Orange Hawkweed (Hieracium aurantiacum) Sunflower Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 

Orange Hawkweed (Hieracium aurantiacum) Sunflower Family

• A perennial with colorful orange-red flowers about one inch 

in diameter. Flower heads are red on the edges and orange 

in the center. Flowers consist of ray florets only with notched 

upper margins. Leaves clustered in a basal rosette. A few 

small leaves may be found on the 6 to 8 inch long stem, but 

often stems remain leafless. Leaves are covered with soft 

white hairs. Stems have shorter dark colored hairs. Leaves 

are darker green on the upper surface than the lower surface. 

Stems 2 to 12 inches, occasionally growing to two feet. Milky 

juice produced by leaves and stems. 

• Spreads by stolons, rhizomes, and seed. A favorite flower of 

unwary gardeners and wildflower enthusiasts. Found along 

roads, riparian areas and beaches.

• Moves into forb meadows and wetlands where it spreads 

aggressively. Forms dense mats, crowding out native plants.
Non-Native Yellow-flowered Hawkweeds Sunflower Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 11

Non-Native Yellow-flowered Hawkweeds Sunflower Family 

Meadow Hawkweed (Hieracium caespitosum)

Mouse-ear Hawkweed (H. pilosella)

Narrowleaf Hawkweed (H. umbellatum)

Common Hawkweed (H. lachenalii)

• Both native and non-native species of hawkweed exist 

in Alaska. Native Alaskan hawkweeds lack stolons, have 

branched stems with many leaves, and generally are found in 

high-elevation meadows.

• Mouse-ear hawkweed has a solitary yellow flower.

• Similar in appearance to orange hawkweed, meadow 

hawkweed grows to 3 feet, its stem covered in coarse black 

gland-tipped hairs, and bearing multiple yellow flowers.

• Narrowleaf hawkweed has hairy leaves with serrated margins.

• Common hawkweed has 7-10 stem leaves that are strongly 

toothed and tapering to the narrowing stem.
Narrowleaf Hawksbeard (Crepis tectorum) Sunflower Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 13

Narrowleaf Hawksbeard (Crepis tectorum) Sunflower Family 

Related Species: Smooth Hawksbeard (Crepis capillaris), is 

another invasive species.

• Annual or winter annual to 3 feet tall. Basal leaves are stalked 

and lance-shaped with margins varying from numerous 

backward-pointing teeth to deeply lobed. Stem leaves clasp 

the stem. Leaf margins are often curled back towards the 

midrib. Bracts below dandelion-like yellow ray flowers are 

smooth, lacking hairs.

• Often found on disturbed soil; waste places, riverbars, or 

roadsides. Thrives in dry, coarse soil.

• Competes with seedlings, forages, cereals and oilseeds. 

The most serious infestations of this weed occur in weak 

crop stands. Spreads into riparian areas.
Hairy Catsear (Hypochaeris radicata) Sunflower Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 15

Hairy Catsear (Hypochaeris radicata) Sunflower Family 

• Perennial herb with a basal rosette of dandelion-shaped 

leaves. Similar in appearance to dandelion, but can grow to 

2 feet. Leaves are densely hairy on both sides. No leaves on 

stems. Several simple or branched stems 6 to 24 inches tall. 

Yellow flower heads, often several heads per stem.

• Grows in meadows, gardens, roadsides, and waste places. 

Especially common in southern Southeast Alaska.

Similar Species: Fall Dandelion 

(Leontodon autumnalis), is a 

similar-looking exotic species 

now spreading in Southcentral 

Alaska. However, fall dandelion 

blooms later in the season.

Fall Dandelion
Perennial Sowthistle (Sonchus arvensis) Sunflower Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 17

Perennial Sowthistle (Sonchus arvensis) Sunflower Family

Related Species: Common Sowthistle (Sonchus oleraceus)

Spiny Sowthistle (Sonchus asper)

• Perennial with flowers and leaves similar to the dandelion. 

Plants to 4 or 5 feet tall. Flower heads are 1 to 2 inches 

across. Long stems arise from a basal rosette of dandelionlike leaves. Stems are branched only at the top. Basal and 

stem leaves have prickly margins. Leaves on the stem are less 

numerous, and clasp the stems at the base. Plants exude a 

milky sap when broken. Bracts below flowers have numerous 

gland tipped hairs 

• Commonly found in waste areas, meadows, woods, lawns, 

roadsides, beaches, ditches, and river and lake shores.

• Can drastically reduce crop yields in agricultural areas 

by displacing native plants on beaches and in meadows, 

competing with desired plants for nutrients.
Common Tansy (Tanacetum vulgare) Sunflower Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 19

Common Tansy (Tanacetum vulgare) Sunflower Family

• Perennial, spreads by seed and by short rhizomes, forming 

dense clumps. Flat-topped clusters of button-like yellow 

flowers. Numerous composite flower heads (20 to 200 per 

plant). Heads composed of disc florets only- flower heads 

without petals. Upright stems often purplish-red and dotted 

with glands. Leaves alternate and deeply divided into narrow 

individual leaflets, giving a feathery appearance. Plants grow 

to five feet tall. Strong odor reminiscent of creosote.

• Thrives in disturbed habitats in full sun. Found on roadsides, 

river and stream banks, and beach meadows.

• Mildly toxic to grazing animals. This plant can grow along 

streams and restrict water flow.
Tansy Ragwort (Senecio jacobaea) Sunflower Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 21

Tansy Ragwort (Senecio jacobaea) Sunflower Family 

• Short-lived perennial with one to several stems arising from 

a taproot. The plant grows 1 to 4 feet tall. Leaves deeply 

cut. Basal leaves stalked 2 to 8 inches long. Leaves become 

smaller and petioles become shorter moving up the stem. 

Flower heads borne in terminal clusters, heads consist of 

yellow ray and disc florets. Ray florets number 10 to 13. Petals 

are 0.25 to 0.5 inches long.

• Forms a low-growing rosette in the first year. Found in waste 

places, roadsides, clearcuts, meadows.

• Contains a toxic compound responsible for considerable 

livestock mortality. It is estimated that the state of Oregon 

has lost $7 million per year to livestock poisoning by this 

plant.
Western Salsify (Tragopogon dubius) Sunflower Family Powell, Dave, USDA Forest Service. Image 1205020. invasive.org.
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 23

Western Salsify (Tragopogon dubius) Sunflower Family

• Biennial or occasionally annual, growing 1 to 3 feet tall, with a 

long, stout taproot. The hollow stem, and long, narrow grasslike leaves contain a milky white juice. Stems are swollen 

immediately below yellow ray flowers. Bracts are distinctly 

longer than the yellow flower petals. Dandelion-like seeds are 

wind dispersed. Juvenile plants resemble shoots of grass. 

Flower heads open and point toward the sun in the morning, 

following it until midday before closing again.

• Occurs along roadsides and disturbed sites. A large population 

has become established along the Turnagain Arm segment of 

the Seward Highway, and is spreading rapidly despite control 

efforts. This species has also been found in Fairbanks and on 

Prince of Wales Island.

• High densities of this plant are likely to inhibit growth and 

recruitment of native forbs and grasses.
Japanese Knotweed Buckwheat Family 

(Polygonum cuspidatum)
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 25

Japanese Knotweed Buckwheat Family 

(Polygonum cuspidatum, P. bohemica)

• An herbaceous perennial that forms extremely dense stands, 

shading out competing vegetation. Stems to 10 feet tall, 

hollow, bamboo-like with thickened nodes where the leaf stalks 

meet the stem. Leaves broadly oval, to 6 inches long, with 

short petioles. Branched sprays of small white to greenishwhite flowers in late August/September. Giant knotweed (P. 

sachalinense) is similar in appearance but has much larger 

leaves and stems. 

• Herbaceous perennial. Dies back, turning bright yellow 

before dropping leaves in the fall. Reproduces from extensive 

spreading rhizomes or broken-off pieces of stem. Found on 

roadsides, stream banks, and beach meadows.

• Clogs waterways and lowers quality of habitat for wildlife, 

fish, and the insects on which fish depend. Displaces 

native salmonberries and thimbleberries along shorelines.
Garlic Mustard (Alliaria petiolata) Mustard Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 27

Garlic Mustard (Alliaria petiolata) Mustard Family 

• Herbaceous biennial plant. Strong garlic odor when crushed. 

First year plants are rosettes of dark green kidney shaped 

leaves arising from a common base with distinct leaf veins and 

scalloped edges to 4 inches in diameter. Second year plants 

with few to several-branched stems to 3 feet tall. Second 

year plants have alternate triangular leaves, decreasing in 

size toward the top of the stem. Flowers white, 0.25 inches 

in diameter, with four petals. Plants flower in April-June with 

seeds produced June-August. Seeds 8 to 10/pod, shiny-black, 

cylindrical. Very tolerant of cool temperatures and low light. 

• Thrives on the moist, shaded soil of river floodplains, forests, 

roadsides, edges of woods, trails, and forest openings.

• Dominates the understory in forested areas. Reduces 

forage sites for deer and other grazing wildlife.
White Sweetclover (Melilotus alba)

Yellow Sweetclover (M. officinalis) Pea family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 29

White Sweetclover (Melilotus alba) Pea Family

Yellow Sweetclover (M. officinalis)

• Annual or biennial; in the first season of growth they produce 

vegetative shoots which may reach 12 inches. Upright growth 

habit. Intolerant of shade. White and yellow sweetclover are 

very similar, differing primarily in flower color. 

• Plants can grow to 6 feet tall, from a taproot. Sweet-scented, 

with many-branched stems. Leaves toothed, oblong to lance 

shaped, and compound with three leaflets. Flowers small and 

white or yellow, in tapering spike-shaped clusters at the end of 

branches. 

• Rapidly colonizes open waste areas, and spreads quickly 

along riparian areas and riverbanks. Already growing 

aggressively along several major Alaskan rivers.
Bird Vetch (Vicia cracca) Pea Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 31

Bird Vetch (Vicia cracca) Pea Family

Related Species: Hairy Vetch (V. villosa)

• Perennial which reproduces by seed and vegetatively by 

underground rhizomes. Multiple, branching vine-like stems 

have small tendrils and alternate, pinnately-compound leaves 

with 8 to 10 leaflets. Bilaterally symmetrical purple flowers are 

arranged on a one-sided spike. Flowering occurs from spring 

to late fall. Seeds contained in inch-long, brown, lance-shaped 

pods.

• Bird vetch aggressively climbs fencing, trees, bushes, 

and other vegetation, monopolizing sunlight, space, and 

moisture. Spreads along roadsides, trails, and other 

disturbed areas.
Scotchbroom (Cytisus scoparius) Pea Family 
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 33

Scotchbroom (Cytisus scoparius) Pea Family 

• Perennial shrub to 10 feet tall from a forked taproot. Stems 

strongly angled. Leaves clover-like, deciduous. Flowers 

numerous, bright yellow, arising from the leaf bases along the 

stem, similar in appearance to garden peas. Fruits pea like, 

flattened, brownish-black. Reproduces vegetatively and from 

seed. Seeds remain viable for up to 80 years.

• Found along forest edges, clearings and meadows. Currently 

found only in southern Southeast Alaska.

• Grows into dense impenetrable stands which prevent 

reforestation, create fire hazard, and eliminate forage for 

deer and other herbivores.
Common Toadflax (Linaria vulgaris) Figwort Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 35

Common Toadflax, Butter & Eggs Figwort Family 

(Linaria vulgaris)

• An aggressive perennial that can reproduce by seeds or 

rhizomes, with 1 to 25 stems per plant. Woody, smooth, erect, 

leafy, often in clumps to 2 feet tall. Numerous pale green 

leaves to 3 inches long, alternate, narrow and pointed at both 

ends. Flowers borne at the end of each stem in spike-like 

clusters, yellow, with central bearded orange patch, one inch 

long, similar to snapdragons with a spur extending below the 

lower lip of the corolla. 

• Common in roadsides, waste areas, lake shores, beach 

meadows, pastures, and edges of forests.

• A persistent, aggressive invader, capable of forming dense 

colonies. Toxic to grazing animals.
Ornamental Jewelweed, Balsam Family

Himalayan Balsam (Impatiens glandulifera)
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 37

Ornamental Jewelweed, Balsam Family

Himalayan Balsam (Impatiens glandulifera)

• Annual herb with thick, many-branched, hexagonally angled 

stems which can grow to 10 feet. Stems smooth, multibranched, reddish in color, but can also be green with large 

swollen nodes and glands at the nodes. Lower leaves opposite 

upper leaves whorled with three leaves to a node. Leaves 

lance-shaped to lance-ovate, 6 inches long, from a stout 

petiole. Leaf margins finely, sharply serrated. Irregular flowers 

one inch in length, pink-purple to white, with five petals.

• Thrives in lowlands, riparian zones, and along beaches. 

• Rapidly clogs streams and wetlands. Prolific seed 

production and aggressive spread make control difficult. 

Unwary gardeners have contributed to its spread into 

Alaska.
Splitlip Hempnettle (Galeopsis bifida) Mint Family 
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 39

Splitlip Hempnettle (Galeopsis bifida) Mint Family 

• Annual which can grow to 4 ft tall. Flowers purple, pink, white 

or pale yellow with dark variegated markings, growing in 

clusters at base of leaf stalks. Stems branched, bristly-haired, 

square in cross section, and swollen beneath the leaf stalks. 

Leaves opposite on stalks, egg-shaped to lance-shaped with 

large rounded teeth and pointed tips. Leaves prominently 

veined and covered with bristly hairs. 

• Forms dense stands on disturbed sites, forest edges, 

riparian areas, meadows, and beaches. Numerous 

seeds are small and easily spread on shoes, tires, and 

recreational equipment. Gardeners quickly come to 

despise this plant.
Reed Canarygrass (Phalaris arundinacea) Grass Family 
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 41

Reed Canarygrass (Phalaris arundinacea) Grass Family 

• Tall reed-like perennial rising from stout rhizomes. Stems are 

hollow, 2 to 6 feet tall, with bluish-green waxy coating. Leaf 

blades flat, up to 3/4 inch wide, with clasping ligules. Leaves 

rough, sheaths open. Panicle inflorescence is 6 to 18 cm long 

with spikelets occuring in clusters on short scabrous branches. 

Seed heads reddish to purplish at base, becoming straw 

colored; compact at first then opening at maturity.

• Highly variable species preferring moist sites. Begins growing 

early in the season.

• Forms dense, persistent, monospecific matted stands. 

Difficult to impossible to eradicate once established. 

Spreads within sites by creeping rhizomes, effectively 

excluding all other vegetation. Found along roadsides, 

ditches, wetlands, riparian areas, beaches, and growing 

into lakes.
Downy Brome (Bromus tectorum) Grass Family

U. of Missouri Cooperative Extension 

Service photo by Fred Fishel.

Alaska Natural Heritage Program photo by Irina Lapina.
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 43

Downy Brome, Cheatgrass Grass Family

(Bromus tectorum)

• Annual or winter annual grass rises 2 to 28 inches from a 

fibrous root system. Seeds germinate in late fall or early 

spring, and rapid spring growth produces mature seed roughly 

2 months later. Seedhead is dense and drooping, and seeds 

range from straw-colored to purplish. Grows in solitary clumps 

or tufts, with light-green leaves, and membranous ligules. Leaf 

sheathes densely and softly hairy. Lemmas have long, soft 

hairs and long awns, giving the grass its “downy” appearance.

• Occurs on rangelands, roadsides, waste places, and disturbed 

sites. Will invade grasslands and open forests, especially 

on sandy or gravelly soils. A highly variable, prolific seed 

producer, adapted to a broad range of site conditions.

• Early maturation and accumulation of dead above-ground 

material greatly increases fire hazard. Awns injure eyes 

and mouths of grazing livestock and wildlife.
Purple Loosestrife (Lythrum salicaria) Loosestrife Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 45

Purple Loosestrife (Lythrum salicaria) Loosestrife Family

• A perennial plant which grows 2 to 8 feet tall. Produces tall 

spikes of purple-magenta flowers, each with 5 to 7 “ruffled” 

petals and a small yellow center. Lance-shaped leaves have 

smooth edges, and are usually arranged opposite one another, 

in groups of 2 or 3 along the stem. As many as 40 stems arise 

from the base of a well-established mature plant. Stems are 4 or 

5-sided in cross-section.

• Purple-pink flower spikes may be confused with Alaska’s native 

fireweed (Epilobium spp.) but in Alaska purple loosestrife blooms 

in the fall, well after fireweed blooms have faded.

• An aggressive wetland invader, purple loosestrife chokes 

waterways, degrading wildlife habitat and fish spawning 

areas. Single plants can produce millions of tiny seeds, 

which are easily spread by wind, water, and wildlife. Wild 

loosestrife is known to hybridize with horticultural varieties. 
Rampion Bellflower (Campanula rapunculoides) Bluebell Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 47

Rampion Bellflower (Campanula rapunculoides) Bluebell Family

• A perennial plant with erect stems which grow 1 to 3 feet tall. 

Numerous purple bell-shaped flowers with 5 teeth have a 

nodding appearance. Leaves are heart-shaped near the base 

of the plant, growing thinner and more lance-shaped further up 

the stem. Leaves are coarse textured with fine, irregular teeth 

on leaf margins. Plants develop white, tuberose roots and a 

network of spreading rootstock. Stems produce a milky sap 

when broken.

• Rampion bellflower spreads by seed and rootstock, 

forming dense patches. Thrives in the open and under 

birch/spruce forest canopy in southcentral Alaska. 

Difficult to control in cultivated and natural areas. Rapidlyexpanding patches spread into lawns and gardens and 

out-compete native vegetation in forests and riparian 

areas.
Species to Monitor:

Siberian peashrub (Caragana arborescens), and European bird 

cherry (Prunus padus), are important ornamental species for the 

nursery and landscape industries in Alaska.

These hardy species are well-suited to Alaskan climates, and make 

good additions to urban yards and landscaped areas. However, 

both species have been observed moving into natural areas, 

outside of cultivation.

Siberian peashrub seedlings have become established in open 

woodlands, meadows, and riparian areas, and European bird 

cherry is now the dominant vegetation along many of the streams 

running through Anchorage greenbelts. The easy establishment 

and rapid displacement of native vegetation by both of these 

species is cause for concern. 

Please be vigilant where these species are planted and cultivated, 

and report their movement into natural areas to the Cooperative 

Extension Service or appropriate local agency.
A dense canopy of European bird cherry along a streamside in Anchorage. In the area pictured here, bird cherry has largely displaced the native 

vegetation, such as willow and birch, on which wildlife depends.
Siberian Peashrub (Caragana arborescens) Pea Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 51

Siberian Peashrub (Caragana arborescens) Pea Family

• Upright branching shrub or small tree with yellow-green bark 

on young twigs. Mature branches and trunk have gray to 

olive-green bark and horizontal lenticels. Leaves are alternate 

or whorled and compound, with 8 to 12 elliptic leaflets, and 

without an end leaflet. Young leaves are light green, darkening 

in summer, and yellow in fall. Stipules are narrow and often 

persist as spines. Yellow tubular flowers are borne on a stalk 

that grows from leaf axil. Fruit is borne in pods; green and 

flattened at first, and sharply pointed, smooth and brown when 

mature.

• A popular ornamental shrub, it forms a dense spreading 

root system, and is now moving into natural areas. A 

known invader of woodlands and riparian areas in Canada 

and the northern United States.
European Bird Cherry (Prunus padus) Rose Family
Forest Service • Alaska Region, April 2007 • www.fs.fed.us/r10/spf/fhp/ 53

European Bird Cherry (Prunus padus) Rose Family

• A low-branched tree which spreads by seed and can reach up 

to 35 feet in height. Produces showy white flowers, borne on 

5-inch long spikes, and a large number of small black bitter 

fruits in late summer. A favorite of some birds, who spread the 

seed along streams. Purplish gray to greenish bark. Leaves 

elliptic to obovate, with sharply serrate margins.

• A favorite ornamental in Alaska. Generally, moose do not 

browse this tree. It is now spreading freely into riparian zones 

in Anchorage and Fairbanks.

• Along urban rivers and streams, it is the dominant 

understory seedling and sapling, replacing native trees 

and shrubs.
Selected Invasive Plant Species of Alaska

COMMON NAME SCIENTIFIC NAME FAMILY PAGE

Canada Thistle Cirsium arvense Sunflower 1

Bull Thistle Cirsium vulgare Sunflower 3

Oxeye Daisy Leucanthemum vulgare Sunflower 5

Spotted Knapweed Centaurea biebersteinii Sunflower 7

(or C. maculosa)

Orange Hawkweed Hieracium aurantiacum Sunflower 9

Non-Native Yellow-flowered Hawkweeds Hieracium Sunflower 11

(pilosella, umbellatum, lachenalii)

Narrowleaf Hawksbeard Crepis tectorum Sunflower 13

Hairy Catsear Hypochaeris radicata Sunflower 15

Fall Dandelion Leontodon autumnalis Sunflower 15

Perennial Sowthistle Sonchus arvensis Sunflower 17

Common Tansy Tanacetum vulgare Sunflower 19

Tansy Ragwort Senecio jacobaea Sunflower 21

Western Salsify Tragopogon dubius Sunflower 23
Japanese Knotweed Polygonum cuspidatum, P bohemica Buckwheat 25

COMMON NAME SCIENTIFIC NAME FAMILY PAGE

Garlic Mustard Alliaria petiolata Mustard 27

Sweetclover, white & yellow Melilotus alba (M. officinalis) Pea 29

Bird Vetch Vicia cracca Pea 31

Scotchbroom Cytisus scoparius Pea 33

Common Toadflax, Butter & Eggs Linaria vulgaris Figwort 35

Ornamental Jewelweed,

Balsam Himalayan Impatiens glandulifera Balsam 37

Splitlip Hempnettle Galeopsis bifida Mint 39

Reed Canarygrass Phalaris arundinacea Grass 41

Downy Brome, Cheatgrass Bromus tectorum Grass 43

Purple Loosestrife Lythrum salicaria Loosestrife 45

Rampion Bellflower Campanula rapunculoides Bluebell 47

Siberian Peashrub Caragana arborescens Pea 51

European Bird Cherry Prunus padus Rose Family 53
Orange hawkweed invading the Kodiak National Wildlife Refuge