Cicuta, commonly known as water hemlock, is a genus of four species of highly poisonous plants in the family Apiaceae. They are perennial herbaceous plants which grow up to tall, having distinctive small green or white flowers arranged in an umbrella shape (umbel). Plants in this genus may also be referred to as cowbane or poison parsnip. Cicuta is native to temperate regions of the Northern Hemisphere, mainly North America and Europe, typically growing in wet meadows, along streambanks and other wet and marshy areas. In the United Kingdom it is frequently found along canals. These plants bear a close resemblance to other members in the family Apiaceae and may be confused with a number of edible or poisonous plants. The common name hemlock may also be confused with poison hemlock (Conium maculatum), or with the Hemlock tree.
Water hemlock is considered one of the most toxic plants in North America and Europe, being highly poisonous to humans. The plant is spread primarily by seeds which are produced in large numbers and are small in size. The type species is Cicuta virosa. The genus is now recognized to comprise four species: Phylogenetic analysis using the sequences of nuclear ribosomal DNA internal transcribed spacer (ITS) loci was not conclusive but seems to show that C. bulbifera and C. virosa are monophyletic, while C. douglasii may not be. It was also suggested a specimen from California may warrant recognition as a distinct species. Other common names for the genus in general include poison parsnip, beaver poison, wild carrot, wild parsnip, and false parsley. while water parsnip has both bracts at the base of flowers and also at the main flower head.
Additionally, there can be confusion between the various water hemlock species and poison hemlock (Conium maculatum) as the common name hemlock is applied to both Cicuta and Conium maculatum. Both are poisonous and can be differentiated by differences in their root structure. Water hemlock has a branched root systems with tubules, while poison hemlock has a single tap root. Cicutoxin is very poisonous, and water hemlock is considered one of North America's most toxic plants. Ingestion of Cicuta can be fatal in humans, and there are reports in medical literature of severe poisoning and death as early as 1670.
The in mice administered cicutoxin by intraperitoneal injection is 48.3 milligrams per kilogram body weight; this compares with 5.9 mg/kg for mice given potassium cyanide by intraperitoneal injection, while the LD<sub>50</sub> for arsenic via intraperitoneal injection in mice is 46.2 mg/kg. The exact toxic dose of plant material in humans is unknown; it is thought ingestion of water hemlock in any quantity can result in poisoning, and very small amounts may lead to death. Intoxication has also been reported following skin contact with the plant; in one case, a family of five rubbed the plant onto the skin and were poisoned, with two children dying. Livestock have long been the worst affected, leading to the common name "cowbane". Poisoning in livestock is common and typically occurs following ingestion of roots of the plant. When the ground is soft in Spring, grazing animals tend to pull the entire plant out of the ground, ingesting both the foliage and the roots. Roots exposed by ploughing can also be the source of livestock poisonings.
Symptoms
Upon consumption, both in humans and other species, the symptoms of poisoning are characterized mainly by generalized seizures. although the rapid onset of seizure activity may be the first sign presented following poisoning. Seizures are usually described as clonic or tonic–clonic. Additional neurological symptoms may include hallucinations, delirium, tingling, pricking, or numbness of a person's skin, dilated pupils, and coma. and alternating low and high blood pressure. Symptoms of excess salivation, wheezing, respiratory distress, and absence of breathing have also been reported. Other ongoing mild effects may include restlessness, muscle weakness, twitching, and anxiety. Complete resolution of symptoms may take a number of days, or these ongoing symptoms may persist for months after poisoning. If a sample of the plant ingested has been retained, diagnosis can be confirmed by having the plant identified by a botanist. Treatment with high doses of benzodiazepines or barbiturates may cause respiratory depression, and respiratory support including intubation and mechanical ventilation is required in these patients. Low blood pressure is usually treated with intravenous fluid replacement, but the administration of dopamine or norepinephrine may be required to restore blood pressure.