Science & Nature • Plant

Poison hemlock

Poison hemlock (*Conium maculatum*) is a highly toxic flowering plant in the carrot family (Apiaceae).

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 27, 2026|2 min read| Fact-checked

Poison hemlock (Conium maculatum) is a highly toxic flowering plant in the carrot family (Apiaceae). Native to Europe and parts of western Asia and North Africa, it has been introduced widely and is now naturalized across much of North America. All parts of the plant are poisonous to humans and many animals, and ingestion can be fatal.

Description

Poison hemlock is a tall, herbaceous biennial with divided leaves and clusters of small white flowers. It is a hairless plant and typically flowers in its second year.

Distribution and habitat

The species is native to Europe, western Asia, and North Africa, but it has been introduced widely and is naturalized across much of North America. It often grows in disturbed, moist, or waste areas such as roadsides, ditches, fields, and pastures.

Toxicity

Poison hemlock contains poisonous alkaloids, especially coniine. Ingestion can cause severe poisoning in humans and livestock, including nervous system symptoms and respiratory failure.

Identification and confusion

The plant is sometimes mistaken for members of the Apiaceae family that are used as food or herbs, including carrot, parsley, parsnip, and wild anise. This resemblance has contributed to accidental poisonings.

Key facts

It is a very poisonous plant in the carrot family.
All parts of the plant are toxic if ingested.
It can be mistaken for edible relatives such as carrot, parsley, or parsnip.
It is an invasive species in many places where it has been introduced.
Poison hemlock is native to Europe and parts of Asia and North Africa.

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Canadian context

Poison hemlock is present in parts of Canada as an invasive toxic weed and is relevant to public health, livestock safety, and invasive-species management.

Frequently asked questions

What is poison hemlock?

Poison hemlock is a highly toxic flowering plant, Conium maculatum, in the carrot family.

Is poison hemlock native to North America?

No. It is native to Europe, western Asia, and North Africa, and was later introduced to North America.

Why is poison hemlock dangerous?

It contains toxic alkaloids, including coniine, and ingestion of even small amounts can cause severe poisoning or death.

Which parts of poison hemlock are poisonous?

All parts of the plant are poisonous, including the leaves, stems, roots, seeds, and fruit.

What does poison hemlock look like?

It is a tall biennial with finely divided leaves and small white flowers arranged in clusters.

Is poison hemlock the plant associated with Socrates?

Traditional accounts identify poison hemlock as the plant used in the execution of Socrates.

References

USDA Agricultural Research Service — https://www.ars.usda.gov/pacific-west-area/logan-ut/poisonous-plant-research/docs/poison-hemlock-conium-maculatum/
Supports: Toxicity, common names, occurrence in North America, poisoning of humans and livestock
U.S. National Park Service — https://www.nps.gov/articles/poison-hemlock.htm
Supports: Native range, introduction as a garden plant, naturalized distribution, high toxicity
Encyclopaedia Britannica — https://www.britannica.com/plant/poison-hemlock
Supports: Species identity, family, native range, biennial growth habit, poisonous alkaloid coniine, Socrates tradition
University of California Agriculture and Natural Resources — https://ipm.ucanr.edu/home-and-landscape/poison-hemlock/
Supports: Invasive status, mistaken identity with crop relatives, toxicity to humans and livestock
USDA Natural Resources Conservation Service — https://www.nrcs.usda.gov/sites/default/files/2022-12/PoisonHemlock.pdf
Supports: Toxic compounds including coniine and other alkaloids