Poison Hemlock Identification

Common Name
Poison Hemlock

Botanical Name
Conium maculatum

Poison hemlock in bloom. Numerous white umbels.  Very similar to several other plants.
Poison hemlock in bloom. Numerous white umbels. Very similar to several other plants.

Identifying Poison Hemlock

Poison hemlock is an herbaceous biennial that can grow up to 10 feet tall, and is one of the most toxic plants in the entire U.S. It can be mistaken for parsley, carrot, water hemlock, wild chervil, Queen Anne's lace, and giant hogweed. The juice of the poison hemlock is said to have killed the ancient Greek, Socrates. The stems are rigid, hairless, branch extensively, and hollow. Reddish purple mottling is common on the lower part of the stem.

Leaves: The leaves are fern-like, pinnately compound, and toothed. They can grow from 8 to 16 inches long and broadly triangular. There are leaf veins that end at the tips of the teeth on the edges of the leaflets. The leaves are shiny green and emit an unpleasant odor when crushed.

Flowers: The flowers are umbels that are 4 to 6 inches across and contain many small, 5-petaled white flowers. The umbels are on individual stems that extend from a common stalk. The flowers bloom from May until August.

Fruit/Seeds: The seeds are 2-joined and distinctly ridged. The seeds are also curved on one side, and flattened to concave on the other side.

Roots: The taproot is white, fleshy, and thick. It can be mistaken for parsnip.

Ecological Threats of Poison Hemlock

Poison hemlock invades roadsides, stream banks, flood plains, woodlands, pastures, and praries. It can quickly colonize disturbed areas as well, and is extremely toxic to humans and animals.

Eradicating Poison Hemlock

Eradication Methods

Mechanical eradication can consist of hand pulling or mowing close to ground level prior to seed dispersal. Either method should be done several times a year for several years.

Chemical eradication can be accomplished with dicamba before buds begin to grow to prevent seeding. Glyphosate can be used to eliminate the entire plant. Always follow herbicide directions closely and use proper personal protective equipment to prevent harm to self, others, and pets.


Toxic Plants Reference Books

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Comments 2 comments

RTalloni profile image

RTalloni 4 years ago from the short journey

Oh dear, is this the same as Queen Anne's Lace?

seh1101 profile image

seh1101 4 years ago from Wisconsin, USA Author

No, it is not. The umbels and taproot are similar to Queen Anness Lace though. I've noticed that Queen Anne's taproot smells just like a carrot, while poison hemlock has a sap-like fluid in the root. Queen Anne's also doesn't grow nearly as tall and thick as poison hemlock.

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