Poison hemlock

Encyclopedia Article

Poison hemlock           Conium maculatum L.

Family: Apiaceae (Parsley family)                         
Life cycle: Biennial
Native status: Introduced
Habitat: Pastures, roadsides, no-till fields             

General description: Basal rosette during first year and then erect flower stalk 6 to 8 ft tall. Leaves are triangular, finely divided and glabrous. Umbels up to 4 in wide with white flowers. Rosettes resume growth in March/April.

Key ID traits: Leaves are triangular in shape and pinnately lobed up to 18" long. Hairless stem with purple spots, often covered with a waxy bloom.    

Similar species: Wild carrot is found in similar habitats, but leaves of wild carrot are pubescent, linear in shape, and more finely divided than poison hemlock.  Poison hemlock is a much larger plant than wild carrot. Water hemlock has a spotted stem like poison hemlock, but is a perennial that produces a cluster of fleshy tubers at crown, and the leaflets are not finely divided like poison hemlock.

Miscellaneous: Poison hemlock contains the toxin coniine which disrupts the central nervous system. Coniine has a structure similar to nicotine. Poison hemlock was commonly used to poison condemned prisoners in ancient Greece, and is believed to be the poison used to kill Socrates.

The deeply lobed leaves of poison hemlock are glabrous and have a triangular shape.

Basal rosettes are present in late summer and early spring. Poison hemlock rosettes are the biggest of the weedy Apiacea species in Iowa, exceeding two feet in diameter.

stems have purple spots and often are covered with a waxy bloom
Stems have purple spots and often are covered with a waxy bloom


Compound umbel with rounded top of individual umbels.

Poison hemlock is much larger than Iowa's other weedy Apiaceae.

Seedlings: wild carrot (L), poison hemlock (C), and wild parsnip (R)