Selected Invasive Plants of Alaska
Selected Invasive Plants of Alaska 2004 United States Department of Agriculture Forest Service, Alaska Region R10-TP-130B Produced by State & Private Forestry, Forest Health Protection 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. Non-native invasive plants displace native vegetation, degrade wildlife habitat, and negatively affect human health, the economy, and the environment. Factors such as geographic isolation and harsh winters have protected Alaska from large-scale invasive plant infestations in the past. Recently, however, some of the most harmful noxious weeds of the lower 48 states have begun to grow and spread in Alaska. Many of the invasive plants featured in this booklet have been responsible for significant economic losses and environmental damage across North America over the past two centuries. Other species featured here (Siberian peashrub and European bird cherry) have been dependable components of Alaska’s urban landscape, but were included because they have recently been observed spreading aggressively into Alaskan wildlands and natural areas. There are many ways invasive plants are introduced to Alaska. Seeds and plant parts can travel in the root balls of nursery stock, in animal feed, tires, recreational equipment, or as components of wildflower seed mixes. Movement of people and equipment within natural areas and site-disturbing projects, such as road-building and construction, can create inroads for invasive plants. Alaskans have the chance to prevent invasive plant infestations before they become so widespread that control is costly and eradication impossible. This invasive plant booklet is designed to assist with identifying some of the most problematic species that are now moving along the roads, streams and beaches of Alaska. Thank you for doing your part to insure that these invasive plant species, and others like them, do not spread into Alaska's wildlands. Photos provided by the Forest Service or the UAF Cooperative Extension Service unless noted. NATIONAL PARK SERVICE UNIVERSITY OF ALASKA FAIRBANKS Department of the Interior College of Rural Alaska Cooperative Extension Service Spotted Knapweed on Turnagain Arm 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 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. For example, spotted knapweed has been found five times within Alaska, but luckily these sites were discovered when the populations were less than 100 plants each. The Alaska Soil and Water Conservation Districts are in the process of forming “Cooperative Weed Management Areas” (CWMAs) across the state. The CWMAs will be actively involved in the detection, monitoring, and treatment of problematic 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://www.uaf.edu/coop-ext http://www.fs.fed.us/r10/spf/fhp/ http://www.cnipm.org/index.html To view or contribute to the state-wide database of exotic plants: http://akweeds.uaa.alaska.edu/akweeds2.html This document was produced by: Michael Shephard, USDA Forest Service, State & Private Forestry Tom Huette, USDA Forest Service, State & Private Forestry Jamie M. Snyder, UAF Cooperative Extension Service (see back pages for index) Canada Thistle (Cirsium arvense) 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. Sunflower Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 1 Bull Thistle (Cirsium vulgare) 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, Haines, POW island thus far. • Restricts recreational land use, decreases land value, and competes with native vegetation for water, space, and light. Sunflower Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 3 Oxeye Daisy (Leucanthemum vulgare) Sunflower Family Oxeye Daisy (Leucanthemum vulgare) • 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. Sunflower Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 5 Spotted Knapweed (Centaurea biebersteinii) (or C. maculosa) Spotted Knapweed (Centaurea biebersteinii) Sunflower Family Sunflower 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, Haines, Valdez and POW island thus far. • Responsible for millions of dollars in economic loss and environmental damage in the western United States. Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 7 Orange Hawkweed (Hieracium aurantiacum) Sunflower Family Orange Hawkweed (Hieracium aurantiacum) • 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 where it spreads aggressively. Forms dense mats, crowding out native plants. Sunflower Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 9 Non-Native Yellow-flowered Hawkweeds Sunflower Family Meadow Hawkweed (Hieracium caespitosum) Mouse-ear Hawkweed (H. pilosella) Narrowleaf Hawkweed (H. umbellatum) Non-Native Yellow-flowered Hawkweeds • 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 is easily identified by its solitary yellow flower. • Similar in appearance to orange hawkweed, meadow hawkweed grows to three feet, its stem covered in coarse black gland-tipped hairs, and bearing multiple yellow flowers. • Narrowleaf hawkweed has hairy leaves with serrated margins. Sunflower Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 11 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. Narrowleaf Hawksbeard (Crepis tectorum) Sunflower Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 13 Hairy Catsear (Hypochaeris radicata) Sunflower Family Similar Species: Fall Hawkbit (Leontodon autumnalis), is a similar-looking exotic species. Hairy Catsear (Hypochaeris radicata) • 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. Sunflower Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 15 Perennial Sowthistle (Sonchus arvensis) Sunflower Family Related Species: Common Sowthistle (Sonchus oleraceus) Perennial Sowthistle (Sonchus arvensis) • Perennial with flowers and leaves similar to the dandelion. Plants to four or five 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 competing with desired plants for nutrients. Sunflower Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 17 Common Tansy (Tanacetum vulgare) 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. Sunflower Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 19 Tansy Ragwort (Senecio jacobaea) 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. Sunflower Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 21 Powell, Dave, USDA Forest Service. Image 1205020. invasive.org. Western Salsify (Tragopogon dubius) Sunflower Family Western Salsify (Tragopogon dubius) • 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. Sunflower Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 23 Japanese Knotweed (Polygonum cuspidatum) Japanese Knotweed (Polygonum cuspidatum) Buckwheat Family • 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 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. Buckwheat Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 25 Garlic Mustard (Alliaria petiolata) 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. Mustard Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 27 White Sweetclover (Melilotus alba) Yellow Sweetclover (M. officinalis) White Sweetclover (Melilotus alba) Yellow Sweetclover (M. officinalis) Pea family Pea Family • 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 six 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. Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 29 Bird Vetch (Vicia cracca) Pea Family Related Species: Winter Vetch (V. villosa) Bird Vetch (Vicia cracca) • 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. Pea Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 31 Scotchbroom (Cytisus scoparius) Scotchbroom (Cytisus scoparius) Pea Family • Perennial shrub to ten 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 eighty years. • Found along forest edges, clearings, meadows, and heath. • Grows into dense impenetrable stands which prevent reforestation, create fire hazard, and eliminate forage for deer and other herbivores. Pea Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 33 Common Toadflax, Butter & Eggs (Linaria vulgaris) Common Toadflax (Linaria vulgaris) Figwort Family • 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. Figwort Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 35 Ornamental Jewelweed, Balsam Family Himalayan Balsam (Impatiens glandulifera) Ornamental Jewelweed, 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. Balsam Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 37 Brittlestem Hempnettle (Galeopsis tetrahit) Mint Family Brittlestem Hempnettle (Galeopsis tetrahit) • 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 edge, riparian areas, meadows, and beaches. Numerous seeds are small and easily spread on shoes, tires, and recreational equipment. Mint Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 39 Reed Canarygrass (Phalaris arundinacea) Grass Family Reed Canarygrass (Phalaris arundinacea) • 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. Spreads within sites by creeping rhizomes, effectively excluding all other vegetation. Found along roadsides, ditches, wetlands, riparian areas, beaches, and growing into lakes. Forms dense, persistent, monospecific matted stands. Difficult to impossible to eradicate once established. Grass Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 41 Downy Brome, Cheatgrass (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. U. of Missouri Cooperative Extension Service photo by Fred Fishel. Alaska Natural Heritage Program, photo by Irina Lapina. Downy Brome (Bromus tectorum) Grass Family Grass Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 43 Foxtail Barley Foxtail Barley (Hordeum jubatum) (Hordeum jubatum) Grass Family • Short-lived perennial grass, reproducing from seeds and tillers. Grows 1 to 2 feet tall, with stems varying from smooth to densely hairy. Initiates growth in early spring, and matures mid- to late-summer. Seedhead is a nodding bushy spike that ranges from pale green to purplish, with multiple, long (1 to 2.5 inch) awns. Stems are slender and erect, with dark nodes, and flat blue-green leaf blades tapering to fine points. Leaves are gray-green and have a sandpaper-like texture. • Found on open ground, in meadows, roadsides, waste places, riparian areas, and other disturbed sites. Awns may cause sores around the eyes, noses, throats and ears of dogs and grazing animals. Grass Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 45 United States Geological Survey, photo by Roseann Densmore. Bluebur (Lappula squarrosa) Bluebur (Lappula squarrosa) Borage Family • An annual or winter annual plant, profusely branched, growing up to 24 inches tall. All surfaces of leaves and stem are covered with stiff white hairs. Lower leaves are oblong and stalked, while upper leaves are smaller, and stalkless. Small five-petaled flowers are pale blue with yellow centers, appearing at the ends of stems, amidst clusters of small leaves. Similar in appearance to forget-me-not (Myosotis) flowers, but smaller.Seeds, or “nutlets,” have two rows of hooked prickles, which attach to clothing and fur for dispersal. • A common weed of roadsides and disturbed areas across the continent. This species is a nuisance to people and animals, as its seeds stick on shoes, clothing, and in fur. Borage Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 47 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, recently both species have been observed moving independently 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) 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. Pea Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 51 European Bird Cherry (Prunus padus) 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 five-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. Rose Family Forest Service • Alaska Region, September 2004 • www.fs.fed.us/r10/spf/fhp/ 53 Selected Invasive Plant Species of Alaska COMMON NAME COMMON NAME SCIENTIFIC NAME CODE FAMILY 27 Garlic Mustard Alliaria petiolata ALPE4 Mustard MEAL12 MEOF Pea Vicia cracca VICRC Pea Cytisus scoparius CYSC4 Pea LIVU2 Figwort SCIENTIFIC NAME CODE FAMILY Cirsium arvense CIAR4 Sunflower 29 Sweetclover, white and yellow Melilotus alba, M. officinalis 1 Canada Thistle 3 Bull Thistle Cirsium vulgare CIVU Sunflower 31 Bird Vetch 5 Oxeye Daisy Leucanthemum vulgare LEVU Sunflower 33 Scotchbroom 7 Spotted Knapweed Centaurea biebersteinii CEBI2 Sunflower 9 Orange Hawkweed Hieracium aurantiacum HIAU Sunflower 35 Common Toadflax, Butter & Eggs 11 Non-Native Yellow-flowered Hawkweeds Hieracium (umbellatum, pilosella, caespitosum) 13 Narrowleaf Hawksbeard 15 Hairy Catsear 17 Perennial Sowthistle HIUM HIPI, HICA10 Sunflower 37 Ornamental Jewelweed Himalayan Balsam Crepis tectorum CRTE3 Sunflower 39 Brittlestem Hempnettle Hypochaeris radicata HYRA3 Sunflower 41 Reed Canarygrass Sonchus arvensis SOAR2 Sunflower 43 Downy Brome, Cheatgrass 19 Common Tansy Tanacetum vulgare TAVU Sunflower 45 Foxtail Barley 21 Tansy Ragwort Senecio jacobaea SEJA Sunflower 47 Bluebur Tragopogon dubius TRDU Sunflower 51 Siberian Peashrub POCU6 Buckwheat 53 European Bird Cherry 23 Western Salsify 25 Japanese Knotweed Polygonum cuspidatum Linaria vulgaris Impatiens glandulifera IMGL Balsam Galeopsis tetrahit GATE2 Mint Phalaris arundinacea PHAR3 Grass Bromus tectorum BRIN1 Grass Hordeum jubatum HOJU Grass Lappula squarrosa LASQ Borage Caragana arborescens CAAR Pea Prunus padus PRPA Rose USDA is an equal opportunity provider and employer. U.S. Fish & Wildlife Service, photo by Leslie Kerr. Orange hawkweed invading the Kodiak National Wildlife Refuge.