Himalayan knotweed (Polygonum polystachyum)
Himalayan knotweed (Polygonum polystachyum)
Himalayan knotweed (Polygonum polystachyum)
Himalayan knotweed (Polygonum polystachyum)

Description
Perennial, blooms July to October. Grows to 6 feet tall. Closely related to Giant and Japanese knotweeds. Leaves are lanceolate and 4 to 8 inches long, unlike Japanese and Giant knotweeds, which are ovate and cordate, respectively.

Impacts
This species is the least common of the three weedy knotweed species in the Pacific Northwest. Plants grow vigorously and create dense colonies that exclude native vegetation, but they...

Houndstongue (Cynoglossum officinale)
Houndstongue (Cynoglossum officinale)
Houndstongue (Cynoglossum officinale)
Houndstongue (Cynoglossum officinale)

Other common names
Hounds tongue, Gypsy flower, Rats and mice, Dog bur

Description
Biennial, blooms June to August. Grows 1 to 4 feet tall; forms rosette the first year and sends up flowering stalks the second year. Leaves alternate, are rough, hairy (resembling a hound’s tongue), and 1 to 12 inches long. Flowers are reddish-purple and terminal. Seeds are nutlets.

Impacts
Houndstongue can be a...

Hydrilla (Hydrilla verticillata)
Hydrilla (Hydrilla verticillata)
Hydrilla (Hydrilla verticillata)

Description
Perennial, aquatic plant. Grows rooted to the bottom with long stems that reach water’s surface. Can be monoecious or dioecious. Leaves are 1/16 to 1/8 inch wide, 1/4 to 3/4 inch long, and occur in whorls of five. Small, axillary leaf scales are found next to the stem and inserted at the base of the leaf, a characteristic that distinguishes Hydrilla from other family members. The nut-like turions (tubers) are a key identifying feature. Egeria densa...

Iberian starthistle (Centaurea iberica)
Iberian starthistle (Centaurea iberica)
Iberian starthistle (Centaurea iberica)

Description
Annual or biennial. Rosettes form in May and June; blooms midsummer through fall. Grows 1 to 6 feet tall. Plant is covered in fine hairs. Leaves are divided into narrow linear segments. Rosettes have spines in the center. Flower heads are purple with straw-colored, spine-like bracts over 1 inch in length. Seeds are plumed, which is the distinguishing factor between this plant and purple starthistle.

Impacts
Closely...

Italian thistle (Carduus phycnocephalus)
Italian thistle (Carduus phycnocephalus)

Description
Annual or sometimes biennial, blooms May to June. Grows 1 to 4 feet tall. Stems have spiny wings. Leaves are deeply cut into 2 to 5 pairs of lobes, have white spots, and the undersurfaces are slightly woolly. Flowers are purplish to pinkish, borne in cylindrical heads either solitary or in clusters of more than 5. Bracts are hairy. Fruits from the outer part of the flower head are gray in color, and those from the inner portion are yellowish to tan....

Japanese dodder (Cuscuta japonica)
Japanese dodder (Cuscuta japonica)
Japanese dodder (Cuscuta japonica)
Japanese dodder (Cuscuta japonica)

Other common names
Giant Asian dodder, Tu Si Zi

Description
Vines are leafless and 1 to 3 millimeters in diameter, with vibrant yellow-green or gold coloration. Purplish spots are also present. The vines contain no chlorophyll. Japanese dodder has thick, spaghetti-like, robust stems, in contrast to native dodder stems which are usually more thread- or string-like. Infestations are often large, spreading, and web-like, covering large...

Japanese knotweed (Polygonum cuspidatum)
Japanese knotweed (Polygonum cuspidatum)
Japanese knotweed (Polygonum cuspidatum)
Japanese knotweed (Polygonum cuspidatum)

Description
Perennial, blooms July to October. Grows four to nine feet tall and has long, creeping rhizomes. Stout stems are reddish-brown, nodes slightly swollen. Leaves are short-stalked, truncate, broadly ovate and two to six inches long by two to four inches wide. Flowers are greenish-white to cream with large, plume-like clusters at the ends of the stems. Hybrids with giant knotweed are common.

Impacts
Japanese knotweed is a...

Johnsongrass (Sorghum halepense)
Johnsongrass (Sorghum halepense)
Johnsongrass (Sorghum halepense)

Description
Perennial that grows three to ten feet tall. Leaf blades are flat with a prominent white midvein. The stems are solid with prominent, swollen nodes. Flowers, or spikelets, are in pairs at the lower end of the flowering stalk, and in threes at the upper end. Johnsongrass has fibrous roots and extensive, thick, creeping rhizomes.

Impacts
Johnsongrass is one of the world’s worst weeds. It is extremely competitive and a...

Jointed goatgrass (Aegilops cylindrica)
Jointed goatgrass (Aegilops cylindrica)
Jointed goatgrass (Aegilops cylindrica)

Description
Winter annual with deep blue-green foliage. Tends to lie flat prior to seed formation. Spikelets are awned, with the longest awns at the top of the spike. Seed heads break into individual segments at maturity.

Impacts
Grows best in cultivated fields, but it can also invade grasslands. It thrives in wheat fields, rangelands, roadsides and fencerows. Ten Jointed goatgrass plants per square yard can reduce cereal crop yields...

Jubata grass (Cortaderia jubata)
Jubata grass (Cortaderia jubata)
Jubata grass (Cortaderia jubata)

Other common names
Pampas grass, Andes grass, Selloa pampas grass, Cortaderia, Pink pampas grass, Purple pampas grass

Description
Perennial grass that ranges 6 to 23 feet tall. Plants have long leaves arising from a tufted base or tussock. The flower cluster is a plumed panicle at the end of a very long stem. Stems generally are at least twice as long as the tussock. Plumes consist of hairy female flowers, deep violet when immature,...