Scientific Name:
Conium maculatum
piperidine alkaloids
Flower Color:
waterside, wetlands, roadsides, wasteareas, fields, haybales

Geographical Distribution

Poison Hemlock distribution - United States

Poison Hemlock

Conium maculatum

Poison parsley, Spotted hemlock, Winter Fern, California fern, Nebraska fern,Wild carrot, Fool's parsley
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Poison hemlock (Conium maculatum) is an annual or biennial herb of the Apiaceae family. It is native to Europe and western Asia but was introduced into North America in the 1800s as an ornamental plant. C. maculatum is now widely distributed across the United States. C. maculatum has small white flowers clustered in large compound umbels that are 1.5-2.5 inches wide. The stem has a hollow, erect, smooth purple-spotted stem that grows 2-10ft in height. C. maculatum leaves are fern-like, large and lacy, alternate and basal, with the upper leaves progressively smaller. When the leaves, stem or flowers are crushed, they produce an unpleasant, parsnip-like odor.

Toxic components
C. maculatum contains eight piperidine alkaloids, however y-coniceine and coniine are generally the most abundant and the predominant cause of acute and chronic toxicity in poultry. Coniine is a pyridine derivative similar in structure and function to nicotine. C. maculatum toxicity varies depending on the stage of growth, environmental conditions (rain, temperature, cloud cover), and soil. Toxicity increases throughout the growing season, especially in the roots, which resemble parsnips. Although all parts of C. maculatum are toxic, the most toxic parts are the fruits when they are still green, and stems.


  • Salivation
  • weakness
  • nervous signs
  • paralysis
  • diarrhea
  • reduced growth
  • hepatic congestion
  • enteritis


MECHANICAL: Mow prior to seed production. Hand pull only while wearing gloves as the plant is highly poisonous.

BIOLOGICAL: Hemlock moth, a defoliating moth, gives inconsistent but sometimes good control.

CHEMICAL: Use a broadleaf weed killer such as 2, 4-D to protect bank-stabilizing grasses. Make sure the chemical is labeled for use around water when poison hemlock is growing in a ditch, stream, or wetland.