Water hemlock, sometimes called cow-bane or beaver-poison, is one of the most toxic plants in the United States. This native species and member of the family Apiaceae contains a toxin that effects the central nervous system when ingested. All parts of the plant are toxic. However, the roots and tubers contain the highest concentration of toxin. Eating even small quantities may cause convulsions, unconsciousness, and death. Cattle find the young tubers especially attractive and may succumb to the plants= poison while foraging. The roots of water hemlock, which resemble parsnips, are sometimes eaten accidentally by humans. Even small amounts are deadly so care should be taken to ensure that these plants are not harvested as food.

Water hemlock is often confused with elderberry shrubs which look very similar but have opposite leaves and white pith. Hemlock leaves are alternately-arranged and lack the white pith. Cutting a small, length-wise slice in a branch to examine the pith is a useful way to differentiate between the two plants. Water hemlock plants will also show distinctive purple striations along the stems. 

The shrubs regenerate from both seeds and tubers and sometimes grow into extensive mats of shrubbery along the shallow, wet margins of wetlands. The attractive white, flat-topped floral clusters are a common sight near swamps and shorelines in the late spring and early summer.

Water hemlock is found from Virginia south into Florida and west as far as Texas.

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