Water Hemlock
Water hemlock (Cicuta spp.) is extremely toxic, causing violent convulsions and sudden death within hours of consuming even a small amount. It is a stout, erect, hairless perennial growing to a height of 4 to 6 ft (1.2 to 1.8 m) from a close cluster of two to eight thick tuberous roots. At the base of the hollow stem is a series of tightly grouped partitions containing an acrid yellow fluid. The leaves are alternate and 1 to 3 times pinnate; the lanceolate leaflets are 1 to 4 inches (3 to 10 cm) long, with toothed edges. The flowers are white and form a loose compound umbel. The flowers have a stylopodium and evident teeth. The fruits are oval and flattened laterally with prominent ribs. There are many species of Cicuta, but C. maculata found in the eastern half of North America, and C. douglasii in the western half, predominate, preferring wet meadows, riverbanks, irrigation ditches, and water edges, often with their roots underwater.
The toxin in water hemlock is cicutoxin, a highly unsaturated alcohol and one of the most poisonous compounds known. All animals, including people, can be fatally poisoned by eating as little as 0.1 to 0.2 oz/100 lbs (50 to 110 mg/kg) body weight of the plant. The lethal dose of fresh green C. douglasii for an adult horse is about 1/2 lb (250 g). All parts of the plant, including the fluid found in the hollow stems, are toxic. However, the roots are even more toxic, as the toxin is concentrated in them. The roots are easily pulled up, as the ground is usually wet. Livestock consuming a single root are usually fatally poisoned. The plant remains toxic when dry, although the mature leaves in late summer seem to have minimal toxicity to cattle. The roots, however, are highly poisonous at all times, with 0.5% body weight of roots, wet weight, being fatal to horses.
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Cicutoxin is a potent neurotoxin causing rapid onset of muscle tremors and violent convulsions. Salivation, vigorous chewing movements, and teeth grinding are common. During the convulsions, animals have been known to bite off their tongues. Signs appear within a few hours of eating water hemlock and progress rapidly to convulsive seizures. Poisoned animals have dilated pupils and progress to a state of coma before dying from respiratory paralysis and asphyxia.
There is no specific antidote to cicutoxin. Animals are usually heavily sedated to reduce the severity of the convulsions, and laxatives are often given to remove the plant from the digestive system.
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