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. The plant is now widely distributed across the United States. It 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. Poison hemlock's 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
Poison hemlock is highly toxic to all animal species, including humans. All parts of the plant contain several piperidine alkaloids, which when ingested, are rapidly absorbed from the gut into the bloodstream. The alkaloid initially has a stimulating effect, followed by a longer-lasting depression of nerve function.


  • muscle weakness
  • dilated pupils
  • trembling
  • ataxia
  • respiratory failure
  • blue-purplish comb
  • characteristic musty mousy odor on the breath and in the droppings
  • rapid pulse


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.