Poison Hemlock occurs in many areas of lowland Weber County and throughout the West. It is a biennial native to Europe that grows 6 to 8 feet tall with an occasional plant reaching 10 feet tall. It is found on borders of pastures and cropland, and in its favorite spot along streams and ditchbanks as pictured to the right. Poison hemlock tolerates poorly-drained soils and will even invade perennial crops such as alfalfa. Its stems are erect, stout, and purple-spotted, with distinct ridges and it is extensively branched. The spots on the stem, and fine, pinnately-divided leaves are features that mark the difference between Poison Hemlock and its more toxic relative, Water Hemlock.

The leaves on Poison Hemlock are shiny green and leaflets are segmented and reach 1/8 to 1/4 inch in length. Lower leaves on long stalks clasp the stem; upper leaves are on short stalks. Its foliage has a strong, distinct, parsnip odor. Flowers are borne in many umbrella-shaped clusters, each supported by a stalk. All parts of the plant are poisonous, including the large white taproot. Humans have been poisoned by mistaking the plant for parsley.