poison-hemlock USDA PLANTS SYMBOL: COMA2
Conium maculatum L.
Synonym(s): poison hemlock, deadly hemlock, poison parsley

Poison hemlock is a biennial (usually) herb that can grow from 3-10 ft. (1-3 m) in height. Stems are hollow, ribbed and purple-spotted. Plants begin as a rosette of leaves and flower in the second year of growth. Leaves are opposite, finely dissected, 8-16 in. long, triangular and emit a foul odor when crushed. The petioles often sheath the stem. Flowering occurs from May to August, when many umbrella-shaped heads (umbels) of small, white flowers develop at the apex of the stems. Umbels are 2-2.5 in. (5-6.2 cm) in diameter and contain many 5-petaled flowers. One plant can produce over 30,000 seeds. Plants, when eaten, are poisonous to most animals. Poison hemlock is native to Europe and was introduced into North America in the 1800s as an ornamental. Poison hemlock can sometimes be confused with water hemlock (Cicuta maculata) and giant hogweed (Heracleum mantegazzianum). The leaf veins in water hemlock end in the notches between the teeth of the leaflets and in poison hemlock the veins end at the tips of the teeth. Giant hogweed has larger, less divided leaves and a hairy stem.

Identification, Biology, Control and Management Resources