Poison Hemlock

Some plants are out to kill you and hemlock is one of them.

Poison hemlock, also known as poison parsley and California fern, is not related to hemlock trees, but it does look an awful lot like a carrot gone to seed.

Poison hemlock (USDA) Public Domain

Flowering carrotr

Poison hemlock (Conium maculatum) is a member of the Umbrelliferae (or Apiacea) family, making it cousin to parsley, celery, parsnip, dill, cumin, fennel, and carrot. All of these herbaceous, biennial plants have flower structures that look like flattened umbrellas. Native to Europe, poison hemlock was brought to the U.S. in the 1800s as an ornamental and is now found throughout the country. Whoops.

A deadly fern

All parts of the poison hemlock plant are extremely poisonous. In 399 B.C., Socrates was found guilty of heresy and corrupting the minds of Athenian youth. For this, he was sentenced to death by drinking poison hemlock. The alkaloids found within poison hemlock cause paralysis of several organs, including the respiratory system, usually within 2 or 3 hours. Eating only a tiny bit of the toxins found in poison hemlock can cause death. People with skin sensitivities may experience irritation by brushing against the plant, but eating it CAN kill you.

Poison hemlock identification

Poison hemlock looks a lot like both domestic and wild carrots, or Queen Anne’s Lace. Unlike Queen Anne’s Lace (Daucus carota) and domestic carrots, which have hairy stems and leaves, the leaves and stems of poison hemlock are smooth. Plants can reach 10 feet in height. The root, which looks a lot like a carrot, is pale yellow or white. It often smells like a mousy parsnip. Purple or red streaks or spots on slender, hollow stems is a clear sign that you are looking at poison hemlock. Stems may also have a white bloom that is easy to rub off. (Just be sure to wash your hands thoroughly afterwards!)

Poison hemlock stem (King County) Public Domain

​There are many branches and the plant often has a wispy, feathery appearance. Leaves are triangular and divided into many fractal iterations of the overall shape. Small, white, clustered flowers normally appear April through July. For comparison, carrot flowers tend to be more pink, but not always. Poison hemlock seeds are held within gray, ribbed fruit, in pairs.

Carrot leaf (left) and poison hemlock (right) image courtesy of World Carrot Museum

​Poison hemlock population explosion

Poison hemlock often grows alongside creeks and in locations with shade and moist soil. Many areas, including Cupertino’s McClellan Ranch Park and the Trukee River, see population booms after wet winters. Seeds (of many different plants) that had been dormant for several years use that moisture to germinate, rushing to reproduce. Just don't be fooled by this deadly plant's delicate appearance.

Just as the “leaves of three, let it be” rhyme has provided years of protection from poison ivy, try embedding this rhyme in your brain to help you stay away from poison hemlock:

Stems so smooth with purple streaks 
Flowers white, a deadly stink

If you suspect poisoning from this plant, call Poison Control immediately at 1-800-222-1222. A quick response can save a life.

UPDATE:

Thanks to John, curator at the Carrot Museum,  I have learned that poison hemlock, for all its toxicity, is also used as a medicine. Seeds, roots, and leaves, when handled properly, can be used to treat respiratory conditions, such as whooping cough, asthma, and bronchitis. Poison hemlock has also been used to treat painful joints, to counteract anxiety and epilepsy, and to reverse strychnine poisoning.