Water Hemlock
A Deadly Poisonous Plant

water hemlock drawing

By Michelle M. Peziol

Water hemlock (Cicuta spp.) is one of the most deadly poisonous plants in North America. When you begin learning about wild plants, a great place to start is with the most dangerous species found in your area. This way you can be sure to avoid these poisonous plants when out in the field learning about other species.

Caution: Water hemlock can be deadly. It contains a toxin called cicutoxin, a violent convulsant, which acts as a stimulant in the central nervous system. Ingestion of hemlock can be fatal and symptoms can occur 15 minutes to 6 hours after the plant has been ingested.

Initial symptoms may include the rapid onset of seizure activity along with nausea, vomiting, muscle twitch, increased pulse, excessive salivation or frothing at the mouth, and dilation of the pupils. Deaths usually occur from respiratory paralysis a few hours after ingestion.

water hemlock leaf

Identifying Water Hemlock

Description: A perennial plant that grows to a height of 3 to 7 feet tall. The leaves are up to 15 inches long, alternately-arranged, and tri-pinnately-compound with numerous 2 to 5 inch ovate leaflets. They are also sharply toothed. The leaf veins terminate at the bottom of leaf serrations and not at the tips, which helps to identify this plant.

water hemlock flower head

Flowers are white and tiny, have 5 petals and 5 stamens that grow in umbrella like clusters 2 to 8 inches across. The plant flowers in spring or early summer. The stem is branching, smooth, hollow and often with purplish-green striations. It has a tuberous root with rootstalks that are multi-chambered and contain a yellowish oily liquid. This poisonous liquid is said to smell like raw parsnip.

Types of Water Hemlocks: bulblet-bearing w. h. (Cicuta bulbifera) , western w. h. (Cicuta douglasii), beaver poison (Cicuta maculata), cowbane (Cicuta virosa), spotted w. h. (Cicuta occidentalis)

Other Common Names: Spotted cowbane, muskrat weed

Family:: Apiaceae (formerly Umbelliferae) - commonly known as carrot or parsley family

Habitat and Range: Typically a wetland plant, common on pastures or tilled areas. This plant occurs in wet, fertile soils at the edge of waters, along streams, and irrigation canals. It is most common in deep loam, clay loam, or clay soils. These hemlock species are found throughout North America and Europe.

Similar species: Poison hemlock (Conium maculatum) is sometimes confused with the water hemlock. Differences are in the root and leaf structure - poison hemlock has a single tap root and the leaf veins run through the tips of the leaf serrations.

Water parsnip (Sium suave) like hemlock grows in similar habitat near water edges. Both have clusters of white flowers, water parsnip has bracts (leaf like structures) at the base of flowers and the main flower head, where water hemlock only has bracts at the base of each small flower cluster. Another way to differentiated water parsnip from hemlock is that its leaves are once compound whereas water hemlock's leaves are three times compound.

Yarrow (Archillea millefolium) has a similar flower structure as water hemlock however its leaves and stem have a hairy appearance. Hemlock's leaves and stem are smooth.

Other: Historically, it is said that some Native American tribes once used hemlock to poison tips of arrows for hunting purposes.

Managing Poisonous Hemlocks - University of Nevada
Water Hemlock - USDA
Lacy White Flowers: The Good, the Bad and the Deadly

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