Plant Profiles Poison Hemlock

Most people will probably recognize hemlock as the poison that Socrates was ordered to drink when he was found guilty of refusing to recognize the official gods of the time and of corrupting youth. Poison hemlock is a member of the parsley family and, although native to Europe, can be found today growing throughout the United States. It is listed as an invasive weed in several states.

The toxic ingredients in this plant are piperidine alkaloids, specifically coniine and coniceine. These are potent neurotoxins that induce paralysis of the motor nerve endings including those used for respiration. There is no recognized antidote. All parts of the plant are poisonous, but the seeds contain the highest concentration of the alkaloids.

The scientific name is conium maculatum: “conium” is a Greek reference to the hemlock itself, and “maculatum” refers to speckles or spots. It has a variety of nicknames, such as devil’s porridge or poison parsley. It has no relation to a hemlock tree.

Poison hemlock tends to grow in wet or poorly-drained areas such as roadsides, field borders, or along railroad tracks. The plant grows to a height of about eight feet, but can grow taller in wet conditions. It has a smooth main stem with red or purple spots and extensive branches. The leaves grow pinnately, meaning the leaflets grow in pairs on opposite sides of a main leaf stalk, which can be up to twenty inches long. The appearance of the leaves is lacy and fern-like. The white flowers grow in an umbrella shape about two inches across. The plant has an unpleasant odor, sometimes described as smelling like a mouse.

Poison hemlock reproduces only by seed. The seeds grow in small ribbed capsules and often fall near the parent plant. Germination of these seeds creates large concentrations of the plant in small areas.

Poison hemlock is sometimes confused with wild carrot (Queen Anne’s lace), which is in the same family. It can be distinguished from wild carrot by the lack of hairs on the stems and leaves of the hemlock. It can also be confused for cow parsnip, but cow parsnip has a palmate leaf arrangement and lacks the red or purple spots on the stem. Most human poisonings occur due to mis-identification of poison hemlock as one of these other plants.

Livestock poisoning is quite common and it affects all types of livestock. Cattle, goats, and horses are most susceptible, but due to its unpleasant taste and smell, animals will not normally choose hemlock if other forage is available. It is important for farmers to monitor their fields for the presence of this plant and control growth where necessary. A recent article on warns that poison hemlock growth is especially high this year.

If you’re out and about in the woods and fields, don’t touch anything unless you’re sure what you’re handling. Sensitive skin can react to simply touching poison hemlock. Despite its attractive appearance, this is a plant to keep at a distance.