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Any of several poisonous herbaceous plants of the parsley family, especially Conium maculatum, believed to be the plant that killed Socrates. It is now common in the U.S. as well as in Europe. A tall biennial, this plant has green stems spotted with red or purple, large compound leaves, and white flowers. Though the poison is concentrated in the seeds, the entire plant is dangerous to livestock when fresh. Despite their common name, poison hemlocks are not conifers (seehemlock). Water hemlocks (Cicuta species) are similar and also dangerous.
This entry comes from Encyclopædia Britannica Concise. For the full entry on poison hemlock, visit Britannica.com.