Water hemlock is a common, widespread member of the carrot family, and it is the most toxic plant in North America. All parts are deadly. A piece of root the size of a walnut can kill a cow-sized animal.
Common water hemlock is a tall, vigorous perennial plant with many leafy branches. The stems are stout, upright, and sometimes spotted or mottled with purple toward the base; the surface is smooth and hairless and sometimes has a white, waxy coating.
The leaves are alternate, compound, the lower ones to 1 foot long and 2 or 3 times pinnately compound; the leaves become progressively smaller up the stem and are 1 or 2 times compound. The leaflets are large, ¾ to 4 inches long, narrowly lanceolate to oblong-lanceolate, sometimes with 1 or 2 basal lobes, the margin usually with teeth. The veins that extend laterally from the leaflet midveins end mostly in the sinuses between the teeth (not at the points of the teeth).
The flowers are minute, with 5 white petals, in compound umbels 2–5 inches across; the umbels arise from the stem tips and as side branches.
Blooms May–September.
- Because this plant is extremely toxic, while several close relatives are considered edible, correct identification is critical for anyone wishing to eat "wild edibles." If you are inexperienced with plant identification, it is best to consider all wild members of the carrot family as potentially fatally toxic.
Similar species: There are several lookalikes in Missouri, some deadly toxic and some edible.
- Poison hemlock (Conium maculatum) is closely related and is also highly toxic. It is very common in Missouri. It can grow up to 9 feet tall and often forms colonies in fields, roadsides, and other disturbed sites. It is not as strongly associated with wet or moist habitats. Its leaves are highly dissected into many small leaflets and look very fernlike.
Height: to 6 feet.
Statewide.
Habitat and Conservation
Occurs in any wet situation in bottomlands: sloughs, banks of streams, rivers and spring branches, margins of ponds and lakes, bottomland prairies, moist depressions of upland prairies, openings of bottomland forests; also roadsides, railroads, and ditches.
This is perhaps the most poisonous of all North American plants, and it is widespread and common. All parts are toxic. Cattle are often the victims.
Status
Native Missouri wildflower. All parts of this plant are extremely toxic if ingested.
Human Connections
All parts of this plant are toxic if eaten. The most toxic parts are the tuberous roots, swollen lower stems, and new growth.
When livestock consume even a little of the plant, either fresh or as a contaminant in hay, they can die within 15 minutes. Poisoned people can suffer similarly.
Ecosystem Connections
Several insects visit the flowers for nectar.
Because it is so toxic, few animals eat this plant. Ingesting just a small amount can kill a cow.
The caterpillars of black swallowtail butterflies eat the leaves and transfer the toxicity to their own bodies; predators learn not to eat them, or any butterflies that look like them.
The toxic chemicals in common water hemlock are different from the ones that are in poison hemlock.
