Poison Hemlock: Another Poisonous Plant Found Throughout the Bay Area

Many people are aware of the dangers of poison oak, but did you know that there are a number of other poisonous plants in the Bay Area? One such plant, poison hemlock (Conium maculatum), commonly inhabits canals, creeks, lakes, and wetlands throughout North America. Fortunately, the U.S. Poison Control has had no confirmed cases of death associated with the species in at least the last 10 years.

Identifying the Plant

By learning to identify the plant, one can more easily avoid it when visiting public open space lands. Poison hemlock can grow from 3 to 8 feet tall and has hollow green stalks which are often spotted with purple or red toward the base. The outline of each leaf is generally triangular in shape and finely divided (similar to the leaves of a fern or Italian parsley). The white flowers grow in rounded heads called umbels, which bloom throughout the summer and produce copious small brown seeds.

Toxic Effects

All parts of the plant are highly toxic when ingested and hands should be washed if the plant is handled. When ingested, the plant’s neurotoxins interfere with the ability to breathe. Poison hemlock can also cause mild to severe skin irritation if the plant abrades the skin, such as during manual weeding without gloves or without long-sleeves. It is advisable to stay out of any large patches of the plant.

Historic Note

The toxic effects of this old-world native species were well known to the Greeks, who used it to administer the death penalty to those convicted of high crimes. Undoubtedly the most famous recipient of this punishment was the philosopher Socrates.

Sources

• Brooks, Daniel (2010). eMedicine, Medscape
• Bronstein A., et al (2008). Annual Report of the American Association of Poison Control Centers’ National Poison Data System (NPDS): 26th Annual Report.
• Wikipedia, the free encyclopedia (2011). Conium.