Water hemlock (Cicuta virosa
) is an erect, branched, leafy, semi-aquatic herb, which is considered one of the most violently toxic plants. It is frequently found directly in the water or on the banks of shallow streams, lakes, creeks, ponds, canals, or ditches.
Water hemlock attributes:
- Height: up to 6 feet
- Stem: Stout, purple-streaked
- Leaves: Alternately placed compound leaves, often a foot long. Consists of numerous lance-shaped, sharply toothed, vein branched leaflets 1 to 5 inches long.
- Flowers: Small white flowers in compound umbrella-like heads are found on the stem and upper most branches.
- Roots: Extend out from the base of the stem; swollen and form tubers 3 to 4 inches long.
All parts of water hemlock contains cicutoxin, a potent neurotoxin, and cicutol, an unsaturated aliphathic alcohol. Cicutoxin acts as a GABA-receptor antagonist, and its action in the central nervous system (CNS) is considered responsible for the highly dramatic and often fatal intoxication following ingestion. Toxicity of water hemlock decreases throughout the growing season; however, the roots remain highly toxic year-round.
Clinical signs usually appear within an hour and death from respiratory failure may occur within a few hours. Due to the acute nature of the poisoning, animals are often found dead not far from the habitat of the plant, where the plant’s roots may have become exposed following a previous drop in the water level.
Most poisoning cases occur during the early stage of growth of the plant, from animals eating the young leaves and stems sprouting from the ground, as in doing so they often pull the shallow tubers out of the soft wet ground and consume them as well. Death is reported in horses ingesting about 2 g/kg of body weight or about 2 lb per 1,000 pound horse.