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 2.5 meters (8 ft) tall, having distinctive small green or white flowers arranged in an umbrella shape (umbel).

[1] Three members of the genus contain a toxin named cicutoxin which causes central nervous system stimulatory effects including seizures following ingestion.

The rootstocks are multichambered and contain a yellowish oily liquid which turns reddish brown on exposure to air and emits a characteristic smell of raw parsnip.

Apiaceae is also known as Umbelliferae, and both of these family names are permitted to be used by the International Code of Nomenclature for algae, fungi, and plants.

[6] 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.

Typically, they grow in wet habitats usually alongside ponds and streams, in marshes or swamps, or areas that are swampy at least part of the year.

[1][3] All members of Cicuta contain high levels of the poisonous principle cicutoxin, an unsaturated aliphatic alcohol that is structurally closely related to the toxin oenanthotoxin found in the plant hemlock water dropwort.

Cicutoxin is present at all stages of growth and in all parts of the plant, but is most concentrated in the roots which appear to be the most toxic in the early spring.

Cicutoxin acts on the GABAA receptor causing a block of the chloride channel which results in neuronal depolarization.

[1][14] Ingestion of Cicuta can be fatal in humans, and there are reports in medical literature of severe poisoning and death as early as 1670.

[20] 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.

[1] Poisoning has been reported following children blowing whistles made from the hollow stem of water hemlock plants.

Initial symptoms may include nausea, vomiting, abdominal pain, tremors, confusion, weakness, dizziness, and drowsiness,[14][26] although the rapid onset of seizure activity may be the first sign presented following poisoning.

[1][27][28] Additional neurological symptoms may include hallucinations, delirium, tingling, pricking, or numbness of a person's skin, dilated pupils, and coma.

[30] Other cardiac effects may include ECG abnormalities such as widening of the PR interval, supraventricular tachycardia, and ventricular fibrillation.

[1][26] Death is usually caused by respiratory failure or ventricular fibrillation secondary to ongoing seizure activity;[1] fatalities have occurred within a few hours of ingestion.

[1] Water hemlock poisoning is usually diagnosed following a history of plant ingestion and symptoms of abrupt onset of seizures.

[35] Decontamination is typically performed only if a potentially toxic amount of plant matter has been ingested up to one hour previously, and the patient has a normal intact airway or has been intubated.

[1] The anticonvulsant phenytoin is not recommended, as it has not been shown to be effective for seizure control following water hemlock poisoning.