Invasive Trees & Shrubs / Bushes in the Pacific Northwest

Himalayan blackberry takes over neglected areas. Plants live for many years (perennial). Canes grow up to 15 feet tall. They grow on the ground or through vegetation or structures.

Himalayan blackberry thorns are large and dangerous. If you are injured by a blackberry thorn, clean the wound with soap and water.

Birds and mammals eat the berries and spread seeds widely.

 Leaves are palm-shaped with a central stem. Each leaf has five leaflets (sometimes three) with toothed margins.

Himalayan blackberry flowers have five petals in shades of white to pink. They are very attractive to honey bees and other pollinators.

Have white, umbrella-like, flowerhead (umbels) that are 18-24 inches across

Stems are 2-4 inches in diameter and hollow. Have purplish-red blotches and bumps. Covered with stiff hairs.

Forms dense patches that emerge in later winter and spring. Stems die and remain standing late summer through early winter.

The leaves grow opposite one another along the red stems.

Leaves grow as long as 15 inches and 11 inches in width. But leaves can be smaller, as shown in the photo.

Flowers are abundant in mid to late summer. They grow on branches in the top 1/3 of the plant. Flowers make seeds that result in new plants. But seedlings play a small role in establishing new stands.

Stems are long, hollow, and segmented like bamboo. They grow from 4-15 feet tall and are often arched.

Knotweed spreads far beyond shoot growth with underground root structures (rhizomes). Stems and root pieces broken or cut away from rooted plants can make new plants.

In the fall and winter, knotweed stems die and remain standing. New growth emerges from the soil in early spring.

Pokeweed often matures into a shrub or small tree. But it is not woody and dies back with the onset of winter.

Stems grow two to eight feet each year from a white, fleshy root. They are colored green, red, or purple. The hollow stems are smooth and grow up to 4 inches across.

Each leaf is 5-20 inches long. The leaves are about one third as wide as they are long. They alternate along the stem. The leaves smell bad when crushed.

The flowers mature into green berries. In late summer or early fall, berries turn dark purple. The berries occur as a drooping bunch that resembles a grape cluster. Berries are poisonous. Do NOT eat the berries.
Birds eat the berries and scatter the seeds. New plants grow from the seeds.

Pokeweed seedlings have alternate leaves. The leaves are red on the underside.

Shoots emerge from established root crowns in the spring. The shoots resemble seedlings, but are thicker and clustered together as shown in the photo.

Mature broom shrubs are three to ten feet tall with dense, slender stems and yellow flowers. Many broom shrubs often grow together.

The flowers are yellow and about 1 inch long, and typical of many plants in the pea family.

Broom species are nitrogen-fixing plants. This trait helps broom grow in areas with poor quality and disturbed soils.

Seed pods (fruits) are hairy along the seam and turn from green to brown as they dry.

A mature Scotch broom plant produces about fifteen thousand seeds per year. The seeds remain viable in the soil for ten or more years.

Scotch Broom Distribution & Reporting in Oregon

Red shows counties in Oregon where Scotch broom is widespread. Yellow shows counties where it has limited distribution. Green shows an area where Scotch broom has been eliminated. Grey areas show counties where it is not known to occur.

Reporting Invasive Species

You can help Oregon agencies track the distribution of invasive species.

If you know about an infestation of Scotch broom, please report it to the Oregon Invasive Species Hotline. Call 1-866-INVADER (1-866-468-2337). Or use the online reporting form.

Butterfly bush establishes in areas with disturbed soil. It grows along roads and riverbanks and in pastures and recently burned areas.

Butterfly bush grows in harsh conditions such as cracks in pavement and gravel roads. The photo shows a butterfly bush growing out of a chimney.

Butterfly bush’s leaves grow alternately along the stems. Leaves are 4-10 inches long and 1-3 inches wide. They are dark green on top and white-pale green underneath.

Flower spikes form at the tip of the branches. Flowers vary in color from white to purple and and blue. The flowers attract butterflies.

Butterfly bush spreads via seeds. Seeds can form during its first year. They are viable for 3 to 5 years.

The photo shows a large, flowering cherry laurel shrub in a landscape.

Leaves grow alternately on stems. They are leathery. The leaves are oval-shaped and 2-8 inches long. The underside of the leaves is lighter colored than the top. Flower clusters grow upright 2-5 inches tall. The white flowers have five petals.

Dark colored berries are about ½ inch wide. Birds eat the berries and spread the seeds.

Common hawthorn grows 6-30 feet tall as a thorny, deciduous small tree or shrub. It often forms a thicket.

Leathery leaves grow alternately on stems. They are 3-7 lobed, 1-2 inches long.
Flowers occur on short stems clustered in flat-topped groups of 10-20. Each flower has five sepals and five white petals that age to light pink.

Common hawthorn flowers are white or pink with five petals. The flowers have a strong odor.

The thorns of common hawthorn are large and dangerous. If you are injured by a thorn, clean the wound with soap and water.

Fruit is a ¼- to ½-inch round, and dark red to crimson that persists into late winter.
Birds eat the fruits and spread the seeds.

Mature gorse shrubs are three to ten feet tall with dense, slender stems and yellow flowers. Many gorse shrubs often grow together.

The flowers are about one inch long and typical of many plants in the pea family.

Gorse spines are large and dangerous. If you are injured by a gorse spine, clean the wound with soap and water.

English holly has waxy, evergreen leaves with spines along the edges. Wear thick gloves and clothing to handle holly plants. The spines hurt.

Red holly berries are about 1/4 inch in diameter. Birds eat the berries and spread the seeds.

There are numerous cultivars of English holly with distinct traits. The photo shows a cultivar with variegated leaves.

Indigo bush is a thornless shrub that loses its leaves in the winter (deciduous). Stems grow roughly 12 feet tall. Plants form dense thickets.

Leaves have a central stem with 13–25 leaflets arranged opposite each other along the stem. The leaflets are one to two inches long, dotted, and hairy.

Indigo bush blooms in May through June. Flowers are showy and lavender-colored. They are densely arranged on erect stems. Flowers are violet to purple with yellow anthers.

Indigo bush spreads by seed and runners from the root system. It thrives along waterways and prairie draws. It also grows along forest edges and rights-of-way.

Indigo bush seeds mature in small fruit pods. Each pod contains 1–2 seeds. The pods float in water to new locations.

Spurge laurel is an evergreen shrub. It grows 2 to 4 feet tall. It has dark green, shiny leaves that grow in dense whorls. Cut stems produce a strong odor.

Small greenish-yellow flowers grow in clusters underneath the leaves. Flowers form in late winter to early spring. Flowers are very fragrant.

Green fruits form in the spring.

Tree-of-heaven is a fast-growing deciduous tree. It grows as a single tree or as many stems as shown in the photo.

Leaves have a large central stem with leaflets arranged opposite each other along the stem. A single leaf is 1-3 feet long.

Established female trees produce hundreds of thousands of seeds each year. The seed forms inside clusters of samaras (seed pods). They remain on the tree through winter.

Mature trees grow as a single trunk up to 100 feet tall. Bark is textured and colored shades of brown and grey as trees age.

Tree-of-heaven has an extensive root system, including shallow roots. The shallow roots produce many shoots that emerge far from the trunk of the established tree.

Tree-of-Heaven Distribution & Invasive Species Reporting in Oregon

The yellow areas on the map of Oregon show counties where tree-of-heaven has limited distribution. Grey areas show counties where it is not known to occur.

Invasive Species Reporting

You can help Oregon agencies track the distribution of invasive species.

If you know about an infestation of tree-of-heaven, please report it to the Oregon Invasive Species Hotline. Call 1-866-INVADER (1-866-468-2337). Or use their online reporting form.

INVASIVE SPECIES ALERT: Spotted Lantern Fly

This invasive insect feeds on tree-of-heaven and damages many agricultural crops. It is established in the Eastern United States. It is not known to occur in the Pacific Northwest at this time. Look for this insect pest and if you find it, report it. Learn more.