Several poisonous plants in the Parsley family, Apiaceae (formerly Umbelliferae) are called hemlock:

• Poison hemlock is a common European plant, Conium maculatum; it contains the alkaloid Coniine.
• Water hemlock was the state poison of ancient Greece.
• Hemlock water dropwort is Oenanthe crocota.

Several other related but edible species are similar in appearance to the above hemlocks, including parsnip and carrot. It is therefore essential that one knows what one is picking, or the results could very well be deadly.

• Quite different from these are the coniferous trees in the genus Tsuga, family Pinaceae. These are not toxic, being called 'hemlock' through a supposed (but not very real!) similarity in the scent of the foliage to that of Conium maculatum.

• Hemlock is occasionally used as a place name (generally in the US because of the tree). see:
  • Hemlock, Michigan
  • Hemlock, Ohio