[Poison Hemlock: The Genus Conium East of the Cascade Mts. of Oregon and Washington]

Poison Hemlock, Poison-hemlock

Conium maculatum

Umbel of poison hemlock from the P Ranch, Malheur NWR.........June 22, 1999.

Portion of a leaf of Poison Hemlock, Poison-hemlock: Conium maculatu

The photo at right shows a leaf of the upper stem of poison hemlock.

Characteristics:

Poison hemlock is a weedy biennial species with one to several upright stems which are freely branched rising from 50 to 300 cm high. The stems are covered with distinct longitudinal ridges and purples spots. The leaves are pinnately divided three to four times into many small leaflets. The larger leaves are commonly 15-30 cm long. The lower leaves clasp the stem while the upper leaves are on long stalks. The foliage has a strong musty odor.

The inflorescence is a compound umbel. The rays of the umbel are subequal, reaching a length of 1-4 cm at maturity. The tiny flowers are white and lack sepals. The paired seeds are several mm long, ribbed, concave in cross-section, and a light brown color.

All parts of this species are highly poisonous. It is the poisonous hemlock species referred to in classical Greek literature.

Habitat:

Poison hemlock is commonly found in moist disturbed places such as the borders of pastures and cropland and along streams and ditches. It tolerates poorly-drained soils.

Range:

Poison hemlock is a native of Europe. It is now established over much of North America. It is fairly common in disturbed places west of the Cascade Mts.

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Poison hemlock observed along the Switchback Trail in a fallow pasture adjacent to the Little Spokane River, Waikiki Springs Nature Preserve, Spokane County, WA......June 24, 2022.

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Close-ups of poison hemlock as seen at the Dyer State Wayside several miles south of Condon, OR.......June 30, 2010.

The photo above shows poison hemlock along the Blitzen River near the P Ranch, Malheur NWR.........June 22, 1999. Plants are up to 3 meters tall and often found spread along streambanks or in roadside ditches.

Purple-spotted stem of poison hemlock.

Paul Slichter