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poison-hemlock	USDA PLANTS Symbol: COMA2 USDA ARS GRIN: 11262 ITIS: 29473 NAPIS: PFFALBA
Conium maculatum L.
Taxonomic Rank: Magnoliopsida: Apiales: Apiaceae
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

Weed of the Week - USDA Forest Service
Element Stewardship Abstract - The Nature Conservancy
Fact Sheet - Pennsylvania Dept. of Conservation and Natural Resources

Selected Images from Invasive.org

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Foliage; the leaf on the right is from poison hemlock (Conium maculatum), and the leaf on the left is from western water hemlock (Cicuta douglasii). Steve Dewey, Utah State University, Bugwood.org Additional Resolutions & Image Usage	Flower(s); Steve Dewey, Utah State University, Bugwood.org Additional Resolutions & Image Usage	Flower(s); John D. Byrd, Mississippi State University, Bugwood.org Additional Resolutions & Image Usage	Feature(s); Purple speckles Steve Dewey, Utah State University, Bugwood.org Additional Resolutions & Image Usage
Feature(s); close-up of main stem Jan Samanek, State Phytosanitary Administration, Bugwood.org Additional Resolutions & Image Usage	Fruit(s); Jan Samanek, State Phytosanitary Administration, Bugwood.org Additional Resolutions & Image Usage	Fruit(s); Jan Samanek, State Phytosanitary Administration, Bugwood.org Additional Resolutions & Image Usage	Plant(s); in flower Jan Samanek, State Phytosanitary Administration, Bugwood.org Additional Resolutions & Image Usage
Plant(s); in flower Richard Old, XID Services, Inc., Bugwood.org Additional Resolutions & Image Usage	Infestation; Eric Coombs, Oregon Department of Agriculture, Bugwood.org Additional Resolutions & Image Usage	Seed(s); Steve Hurst, USDA NRCS PLANTS Database, Bugwood.org Additional Resolutions & Image Usage	Diagram or Graphic; Britton, N.L., and A. Brown. 1913. Illustrated flora of the northern states and Canada. Vol. 2: 653. USDA PLANTS Database, USDA NRCS PLANTS Database, Bugwood.org Additional Resolutions & Image Usage
Diagram or Graphic; USDA NRCS. Wetland flora: Field office illustrated guide to plant species. USDA Natural Resources Conservation Service. USDA PLANTS Database, USDA NRCS PLANTS Database, Bugwood.org Additional Resolutions & Image Usage

Taxonomic References:

USDA, NRCS. 2001. The PLANTS Database, Version 3.1, National Plant Data Center, Baton Rouge, LA 70874-4490 USA.

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