Cicuta douglasii, the western water hemlock, is a poisonous plant in the family Apiaceae. It is a perennial plant that grows in wet places such as marshes, stream banks, slough margins, ditches, meadows, and wet pastures. The roots are thick and tuberous, with many smaller tubers on the main tuber, allowing survival in wet conditions. Water hemlock is most abundant in British Columbia, and is indigenous to North America, where it grows primarily from the base of the Rocky Mountains to the Pacific coast, stretching from Alaska all the way to California. Water requirements limit this plant from inhabiting open rangelands.
Characteristics of water hemlock include its stem, which is 0.5–2 meters tall with purplish spots, thick roots, and alternate leaves that are compound pinnate. The leaflets are usually 5–8 cm long and 1–2 cm wide, with jagged edges. Its inflorescences are compound umbellate with many small, white flowers. There are two seeds per flower. Seed dispersal is by means of wind, water, machinery, clothing, and through transported soil. The seeds germinate in spring, and flowers mature near the end of June and beginning of July. In addition to sprouting new plants from seeds, rootstocks can also produce new plants in the fall from the basal meristem. When these detach the following spring, they may form a new plant.
The main distinguishing characteristic of western water hemlock is its toxicity. Cicutoxin is the toxin that is produced, making water hemlock the most poisonous plant in North America. Cicutoxin is a yellowish liquid that is prevalent in the roots. This unsaturated alcohol has a major impact on the central nervous system of animals. Early symptoms of cicutoxin poisoning include excessive salivation, frothing at the mouth, nervousness, and incoordination. These symptoms can progress to tremors, muscular weakness, seizures and respiratory failure. Ingestion of green materials of western water hemlock in amounts equivalent to about 0.1% of a person's body weight can even lead to death. In addition to being extremely hazardous to humans, this plant has an enormous impact on animals. As little as 0.2–0.5% body weight for sheep, 0.1% body weight for cattle, 0.5% body weight for horses, and 0.3% body weight for swine can be lethal. Death can occur within fifteen minutes of ingesting the toxin. It is one of the first plants to emerge in springtime, and has a very appealing odor. These characteristics, along with the fact that it grows in moist areas, make the plant very attractive, but deadly, to grazing animals.
- Weeds BC (2005-07-13). "Water hemlock, Cicuta douglasii". Archived from the original on 2002-07-30. CS1 maint: discouraged parameter (link)
- Saskatchewan Agriculture and food (2005-07-13). "Western water hemlock". Archived from the original on 2005-10-28. CS1 maint: discouraged parameter (link)
- Block, N. (n.d.). (2005-07-13). "Cicuta douglasii (DC.) Coult. & Rose".
- Schep LJ, Slaughter RJ, Becket G, Beasley DM (April 2009). "Poisoning due to water hemlock". Clin Toxicol. 47 (4): 270–8. doi:10.1080/15563650902904332. PMID 19514873. S2CID 21855822.
- Ministry of agriculture, food & fisheries (2005-07-13). "Western water hemlock". Archived from the original on 2005-08-29. CS1 maint: discouraged parameter (link)