Medusahead rye (Taeniatherum caput-medusae)
Medusahead rye (Taeniatherum caput-medusae)
Medusahead rye (Taeniatherum caput-medusae)
Medusahead rye (Taeniatherum caput-medusae)

Description
Annual, blooms May to June. Grows six to 18 inches tall. Slender annual grass with spikelets in a densely crowded bristly spike one to four inches long. Leaf blades are somewhat rolled, 1/16-inch wide. Usually found in clayey soils.

Impacts
Found in virtually every county in the state, Medusahead rye demonstrates its negative qualities best on the east side of Oregon, where it out-competes other grasses by extracting the...

Mile-a-minute (Persicaria perfoliata)
Mile-a-minute (Persicaria perfoliata)
Mile-a-minute (Persicaria perfoliata)

Description
Herbaceous, annual vine. Delicate stems are reddish, highly-branched and covered with small, curved spines. Circular, leafy structures (ocreae) surround the stem at the base of the petioles. The alternate leaves are triangular, light-green, 1 to 3 inches wide and barbed on the undersurface. Small, white, inconspicuous flowers arise from the ocreae. Fruits, present from mid-July through the first frost, are metallic blue and segmented, with each segment...

Milk thistle (Silybum marianum)
Milk thistle (Silybum marianum)
Milk thistle (Silybum marianum)
Milk thistle (Silybum marianum)

Other common names
Blessed thistle, St. Mary’s thistle, Lady’s thistle

Description
Biennial or winter annual, blooms from April to July. Grows two to six feet tall. Stems stout, rigid and generally branching. Leaves broad, clasp stem, have spiny margins and have white marbling along veins. Flower heads reddish-purple and have leathery spine-tipped bracts.

Impacts
Once established, it forms...

Mouse ear hawkweed (Hieracium pilosella)
Mouse ear hawkweed (Hieracium pilosella)
Mouse ear hawkweed (Hieracium pilosella)

Description
Perennial. Leaves have distinctive white midveins and are covered with long white hairs. It has stolons like strawberries and a fibrous root system. Flowers are produced on a long, leafless stalk and are covered with stiff, dark hairs. Flowers occur in clusters of at least two on top of the flower stalks and are bright yellow in color. Flowers resemble those of a dandelion.

Impacts
This plant produces mats of rosettes...

Musk thistle (Cardus nutans)
Musk thistle (Cardus nutans)
Musk thistle (Cardus nutans)
Musk thistle (Cardus nutans)

Other common names
Nodding thistle

Description
Biennial, blooms in early June. Grows three to six feet tall. Flower heads are large, purple, solitary and usually nodding. Musk thistle has dark-green leaves with light-green midribs and wavy, spiny lobed margins. Leaves have a smooth waxy surface and appear winged at the attachment to stem.

Impacts
Musk thistle is unpalatable to wildlife and livestock,...

Myrtle spurge (Euphorbia myrsinites)
Myrtle spurge (Euphorbia myrsinites)
Myrtle spurge (Euphorbia myrsinites)

Other common names
Creeping spurge, Donkey tail spurge

Description
Perennial, blooms in early spring. Grows 4 to 6 inches tall. Leaves are alternately arranged in close spirals around the fleshy, trailing, blue-green stems. Flowers are inconspicuous and surrounded by a showy yellow-green bract. This plant prefers well-drained dry to moist soils with partial shade to full sun. Mrytle spurge is an escaped ornamental that inhabits...

Narrow-leaved ragwort (Senecio inaequidens)
Narrow-leaved ragwort (Senecio inaequidens)

Description
Perennial, herbaceous or woody shrub, up to 100 centimeters tall, spherically shaped and rising from a shallow taproot. Stems are erect, leafy, rising from the woody base, numerously branched and glabrous, but sometimes sparsely hairy. Leaves alternate, are usually sessile, occasionally petiolate, with the blade bright-green, simple and slightly thickened, usually with the base clasping the stems. Basal leaves are sessile, 3 to 14 centimeters long and 0....

Oblong spurge (Euphorbia oblongata)
Oblong spurge (Euphorbia oblongata)
Oblong spurge (Euphorbia oblongata)
Oblong spurge (Euphorbia oblongata)

Other common names
Egg leaf spurge

Description
Weedy, escaped ornamental species of Euphorbia. An exotic perennial herb that produces up to 20 stems on a woody rootstalk, with the plants reaching nearly three feet high. The alternate, oblong leaves are glabrous (smooth and hairless) with finely toothed margins. Leaves and stems exude a milky sap when cut; skin contact should be avoided. Numerous yellowish-green bracts and flowers...

Old man's beard (Clematis vitalba)
Old man's beard (Clematis vitalba)
Old man's beard (Clematis vitalba)
Old man's beard (Clematis vitalba)

Other common names
Traveler's joy

Description
Perennial, blooms most of the summer. Woody, deciduous vine with stems growing up to thirty yards long. Leaves are opposite and compound, usually with five leaflets. Flowers are small, greenish-white and found in clusters in the upper leaf axils. Long feathery stiles that produce a mass of white during the seed stage are responsible for the plant’s name. The characteristic...

Onionweed (Asphodelus fistulosus)
Onionweed (Asphodelus fistulosus)
Onionweed (Asphodelus fistulosus)

Description
Herbaceous perennial in the lily family. Grows to about a foot tall and almost as wide. Clusters of long, tapering, round, hollow leaves very much resemble chives or scallions. Leaves sprout after winter rains. Flowers appear in the spring. The flat flowers are less than a half-inch across and have six petaloid parts, each white with a pink center line. They are sparsely distributed on branched spikes to almost two feet tall. Fruits are 1/8-inch...