Description:

Bull thistle is a tall, prickly biennial with spiny flowers. The erect plant stands around 2 to 5 feet tall on rigid, hairy, branched stems that usually die back during winter. Rosettes are up to 60 cm wide Bull thistle is native to Europe and Asia and can be found throughout the United States. Bull thistle rosette leaves are green,  hairy, 10-40 cm long, lobed and toothed, elliptical to lanceolate with prickles. Purple disk flowers of the Bull thistle plant are surrounded by rows of spine tipped phyllaries with one bractlike leaf below. Flowers appear from June to October with 1 to 5 heads per branch. Petals are often purple but can be  white. Flowers are found at the end of branches, round to umbrella shaped and are 1.5-2 inches wide.

Life cycle:

Biennial

Height of mature plants

2 to 5 feet

Flower color:

Purple

Bloom time:

Typically blooming from June to October.

Look-a-likes:

There are several native and nonnative thistles that resemble bull thistle. Please see this guide for identification clarification.

Habitat:

Bull thistle colonizes primarily in disturbed areas such as pastures, roadsides, and ditch banks as well as in hayfields, disturbed prairies and logged mountain areas.

Impacts:

Bull thistle may outcompete native plants and desirable wildlife and livestock forage plants. It can invade most any disturbed habitat and grow in dense thickets. Hay price may decline with the presence of bull thistle.

Noxious Weed Listing:

• WeedWise: Maintenance
• State of Oregon: Class B
• State of Washington: Class C
• Four County CWMA: Class C

Origin:

Europe, Asia and Northern Africa

Present in Clackamas County:

Yes

Links:

Oregon Noxious Weed Profile
Washington Noxious Weed Profile
King County Noxious Weed Profile

Description:

Spurge laurel is an evergreen, slow-growing, long-lived, and shade-tolerant woody shrub that grows up to five feet tall. It is a member of the Thymelaeaceae family. The plant is poisonous to humans, cats, and dogs and handling the plant can also cause contact dermatitis. Be sure to wear gloves when handling this plant. It growth in both an upright form and a more sprawling form with many stems emerging laterally from the root crown.

Life cycle:

Perennial

Height of mature plants

5 feet

Flower color:

Green

Bloom time:

February to April

Look-a-likes:

None

Habitat:

Spurge laurel has been found to prefer moderate shade at 12%-15% canopy closure. It is a serious threat in Oregon White Oak woodland and Douglas fir forests in our region. It also affects other forest types and residential properties mostly in more urbanized area of Clackamas County.

Impacts:

Escaped populations from ornamental plantings continue to expand into forested areas especially adjacent to urban areas. As birds further disperse seeds, more habitats will be invaded and native plant communities altered. Oak woodland forests are the greatest at-risk forests because of this and other aggressive weed species. Most plant parts are toxic to humans and contain toxic compounds. Contact with the sap can cause skin irritation and ingestion of the seeds can cause poisoning especially in young children.

Noxious Weed Listing:

• WeedWise: Priority
• State of Oregon: Class B
• State of Washington: Class B
• Four County CWMA: Class B

Origin:

Europe and Northern Africa

Links:

Oregon Noxious Weed Profile
Washington Noxious Weed Profile
Invasive.org profile

Description:

The plant is a well armored summer annual growing 3-4 feet tall. The leaves covered with short white hairs, white-veined above, 1 to 3 inches long and have 2 short lobes and a 3-forked spine at the junction with the stem. Male flowers are segregated from the female by being located in the uppermost parts of the plant and clustered. Female flowers are below male flowers and form a beaked bur that bears many small hooked bristles.

Life cycle:

Annual

Height of mature plants

3-4 feet

Flower color:

White

Bloom time:

July through October

Look-a-likes:

None

Habitat:

Spiny cocklebur is most frequently found in highly disturbed waste areas and barnyards. It surrounds many small reservoirs in Oregon.

Impacts:

The burs of spiny cocklebur can become tangled in the hide or wool of livestock adding to the cost of the woolen product. It is moderately competitive and is a nuisance in hand-harvested crops. The seeds and seedlings of spiny cocklebur are poisonous. The symptoms are anorexia, depression, nausea, and prostration. Death may occur in a few hours to three days after the symptoms are first noted.

Noxious Weed Listing:

• WeedWise: Priority
• State of Oregon: Class B
• State of Washington: Class C
• Four County CWMA: Class D

Origin:

South America

Links:

Oregon Noxious Weed Profile
Washington Noxious Weed Profile
Invasive.org profile

Description:

Scotch broom is a fast growing shrub in the Fabaceae (pea) family, characterized by its masses of yellow flowers. It grows upright on young green, 5-angled stems which are hairy. Broom forms dense stands and are shade intolerant. Mature plants can reach 10 feet in height although most plants are typically 3-5 feet tall. Scotch broom is deciduous nitrogen fixing plant. Scotch broom is an invasive plant found in low elevations from British Columbia to California.

Life cycle:

Annual, Biennial, Perennial

Height of mature plants

4 to 8 feet

Flower color:

Yellow

Bloom time:

April to June

Look-a-likes:

It can be confused with the less common Spanish broom, Spanish broom has fewer round stems, very few leaves, and larger yellow flowers.

Habitat:

The areas most infested by Scotch broom are disturbed (logged or burned) sites, grasslands, open forests, and riparian corridors. The plant likes coastal areas and low elevations in dry conditions with plenty of sunshine. Scotch broom flourishes in infertile soil because it is a nitrogen fixing plant which allows it to grow where many plants cannot. Scotch broom likes sandy, acidic and dry soil.

Impacts:

Scotch broom is a pioneer species known to displace native plants and smother tree transplants increasing tree death or slowing growth in the early years. It readily invades disturbed sites, natural areas, dunes, and forestlands. Broom control costs on right-of-ways, public facilities, parkland and private property are in the millions of dollars each year due to its rapid growth and persistent nature. Scotch broom is a prolific seed producer of long-lived (10 years plus) seeds. Broom stands establish persistent soil-seed banks requiring long-term commitment to exhaust. The costs attributed to Scotch broom come from labor and chemical inputs needed to control infestations ($47 million annually) in timberlands and from lost productivity. Pollen production during bloom time also can be quite an allergen source for allergy sufferers.

Noxious Weed Listing:

• WeedWise: Maintenance
• State of Oregon: Class B
• State of Washington: Class B
• Four County CWMA: Class B

Origin:

Europe and North Africa

Links:

Oregon Noxious Weed Profile
Washington Noxious Weed Profile
Invasive.org profile
CABI Invasive Species Compendium

Description:

Velvetleaf is an annual weed in the mallow family (Malvaceae) that germinates in the spring and flowers in the summer. Heart-shaped, alternate, velvety leaves have long stalks and a distinct odor when crushed. Yellow flowers are followed by persistent, crown-shaped seed pods.

Life cycle:

Annual

Height of mature plants

3-8 feet tall

Flower color:

Yellow

Bloom time:

July-September

Look-a-likes:

None

Habitat:

Open, moist, disturbed areas, roadsides and agricultural lands

Impacts:

Damages agricultural production by competing with crop plants for light and nutrients, and hosting several crop pests affecting tobacco, maize and soybeans

Noxious Weed Listing:

• WeedWise: None 
• State of Oregon: Class B
• State of Washington: Class B
• Four County CWMA: Class B

Origin:

Asia

Links:

Washington Noxious Weed Profile
Invasive.org profile
CABI Invasive Species Compendium

Description:

A bushy herbaceous perennial that may act like an annual in regions with harsh winters. Leaves somewhat succulent, opposite, compound and each having 2 ovals, 1 inch leaflets. Stems smooth and branched from a thickened woody crown. Flowers are small; compact bunches of five petals each with prominent stamens, salmon to yellow or white with pinkish veins and up to ¾ inch. Flower buds have been used as a substitute for capers. It reproduces by seed and vegetatively from lateral creeping roots.

Life cycle:

Perennial

Height of mature plants

18 inches

Flower color:

White

Bloom time:

It flowers from May to August.

Look-a-likes:

None

Habitat:

Syrian bean-caper can be found in open, rocky areas and gravelly soils, including roadsides and disturbed areas.

Impacts:

Syrian bean-caper is well suited to dry environments. Buds and branches form on spreading roots, forming dense patches that compete for water and space. Large infestations can reduce forage potential in dryer areas of the west. It grows in masses, forming colonies, especially in dry, gravely, disturbed areas where other plant life is rare. Hand removal is often unsuccessful due to remaining root fragments that can generate new plants.

Noxious Weed Listing:

• WeedWise: Priority
• State of Oregon: Class A
• State of Washington: Class A
• Four County CWMA: Not listed

Origin:

Syrian bean-caper is native to the Middle East and central Asia.

Links:

Oregon Noxious Weed Pprofile
USDA Plants
Bugwood Wiki
Washington State Noxious Weed Control Board

Description:

Himalayan Blackberry is a tall semi-woody shrub, characterized by thorny stems and edible fruits. It grows upright on open ground and will climb over and trail over other vegetation. Mature plants can reach 15 feet in height. The canes of Himalayan blackberry can reach lengths of 40 feet and are typically green to deep red in color. Himalayan blackberry forms dense, nearly impenetrable thickets. In some instance, canes can reach densities of more than 500 canes per square yard. The canes of Himalayan blackberry typically last only three years before dying off, so dense thickets are often dominated by old canes.

Life cycle:

Perennial

Height of mature plants

Up to 15 feet

Flower color:

White, Pink

Bloom time:

April to August.

Look-a-likes:

Cutleaf blackberry (Rubus lacinatus) is similar but has more deeply divided leaves.

Habitat:

The areas most infested by Himalayan blackberry are disturbed sites and along stream corridors. Blackberry flourishes on open ground, and on unmanaged sites. Plants grown in wet soils tend to be dense and more robust. Due to the movement by birds, Himalayan blackberry also is commonly found under perching sites, such as along fence rows and under power lines.

Impacts:

Himalayan blackberry is a highly invasive plant that replaces native vegetation. The canes of blackberry can build up substantial litter layer which may serve as fuels for wildfire. The thorns of the blackberry plants can limit the access of a site by both animals and people. While dense thickets can be useful to some wildlife species, the diversity of habitats is greatly diminished, thereby diminishing the usability of a site to only a few species.

Noxious Weed Listing:

• WeedWise: Maintenance
• State of Oregon: Class B
• State of Washington: Class C
• Four County CWMA: Class C

Origin:

Asia

Links:

Oregon Noxious Weed Profile
Washington Noxious Weed Profile
Invasive.org profile
CABI Invasive Species Compendium

Description:

Herb Robert is a low growing winter or spring annual or biennial ground cover with lacy, delicate, hairy light green to red spreading stems and leaves. It produces dense mats that choke native flora. Plants grow from short rosettes to about 1 foot tall. The leaves are deeply dissected and light green. The foliage turns red in late fall or in areas with high light exposure. Leaves are covered in glandular hairs, and have a strong odor when crushed, thus the common name ‘stinky Bob’. Stinky Bob has small, delicate, white or pink 5 petal flowers and blooms prolifically throughout the spring and fall. The fruit is a capsule. Seeds are brown and about 2 mm in length. Herb Robert has a very shallow, weak, fibrous root system which makes hand pulling easy.

Life cycle:

Annual, Biennial

Height of mature plants

1 foot

Flower color:

Pink, White

Bloom time:

Spring through Fall

Look-a-likes:

Habitat:

Herb Robert is highly adaptable. It is found especially in moist forests with canopy closure but can also be spotted on dry rocky outcrops and everywhere in between. It’s becoming a significant garden pest in some areas. It is found from sea level to mid-mountainous areas in both the Cascades and Olympics, up to 4000 feet. It doesn’t require disturbance to move into a new area, making it a particular concern for intact ecosystems.

Impacts:

Herb robert invades forests where it displaces native herbaceous species and forms monocultures. It is highly aggressive and quick to spread, even in undisturbed settings and releases allelopathic chemicals which prevent native plants from growing and decreases diversity.

Noxious Weed Listing:

• WeedWise: Maintenance
• State of Oregon: Class B
• State of Washington: Class B
• Four County CWMA: Class C

Origin:

Europe, Asia and Northern Africa

Links:

Oregon Noxious Weed Profile
Washington Noxious Weed Profile
Invasive.org profile
CABI Invasive Species Compendium

Description:

Goatsrue is a perennial herbaceous plant, 2-6 feet tall, with hollow stems and alternate, pinnately compound leaves of 13-21 odd-numbered leaflets. Flowers resemble peas and vary from peach to purple to white. It can produce dense stands. The flowers are pea-like and white to bluish lilac to reddish purple. They are found clustered at the end of stems or in leaf axils.

Life cycle:

Perennial

Height of mature plants

2-6 feet

Flower color:

White, Blue

Bloom time:

Flowers from June to October.

Look-a-likes:

It closely resembles wild licorice (Glycyrrhiza lepidota) and care should be taken to properly identify it before any control measures are taken.

Habitat:

Goatsrue can form monotypic stands in wetlands and marshes, as well as invading cropland, irrigation ditches, pastures, fence lines, and roadways. Prefers full sun but will tolerate some shade.

Impacts:

Goatsrue can displace wetland vegetation, pushing out native plants and reducing food and nesting resources for wildlife. It also contains poisonous alkaloids that can be fatal to humans, sheep and cattle.

Noxious Weed Listing:

• WeedWise: Priority
• State of Oregon: Class A
• State of Washington: Class A
• Four County CWMA: Class A

Origin:

Middle East

Links:

Oregon Noxious Weed Profile
Invasive.org profile
CABI Invasive Species Compendium

Description:

Garlic mustard is a biennial plant in the Brassicaceae (mustard) family. Garlic mustard is an aggressive woodland invader throughout much of the Continental United States. It affects both disturbed and pristine woodlands and has become one of the worst invaders of forests in the American Northeast and Midwest regions. The plant can form dense stands up to 4 ft in height and can aggressively out-compete other native plants. The most identifying set of factors for this plant are its white, cross-shaped (cruciform) flowers and presence of a garlic odor on crushed leaves.

Life cycle:

Biennial

Height of mature plants

Up to 3.5 feet

Flower color:

White

Bloom time:

April through May

Look-a-likes:

Garlic mustard flowers are similar in appearance to those of other species in the Mustard family. Money plant (Lunaria annua) in particular can be confused due both species having the same stature and money plant sometimes having white flowers instead of it’s typical purple. Unlike other similar species, garlic mustard’s leaves smell of garlic when crushed.

Habitat:

Garlic mustard grows best in filtered to partial light. However, in our region garlic mustard can grow in an exceptionally wide variety of habitats including both open and shaded ones as well as upland and stream-side locations. It grows on sand, loam, and clay soils. Where this plant is most abundant in Clackamas County, it is predominantly found near rivers, roadsides, and on non-turf portions of parks and residential properties.

Impacts:

Garlic mustard can invade healthy forests and severely reduce biodiversity through highly successful competition for light. It is thought to produce a toxin that kills soil fungi that other native plants are dependent on, including native tree seedlings.

Noxious Weed Listing:

• WeedWise: Priority
• State of Oregon: Class B
• State of Washington: Class A
• Four County CWMA: Class A

Origin:

Europe

Links:

Oregon Noxious Weed Profile
Invasive.org profile
CABI Invasive Species Compendium