Poison Ivy

Many of you will recognize this rhyme, alerting us to avoid leaves of the plant we commonly know as poison ivy. It draws attention to the distinctive three leaflets that make up poison ivy’s compound three-part leaf. Botanists have assigned this plant the scientific name Toxicodendron radicans, a name that itself warns of poison ivy’s toxic effects. The genus, Toxicodendron, translated from Greek, means “poison tree.” It is derived from two words—toxikos, or “poison,” and dendron, meaning “tree.” The species ending, radicans, comes from the Latin radicor, “to take root.” The common name “poison ivy” highlights the potential toxic effects of contact with the plant’s leaves, which typically produce an intensely itchy skin rash and blisters. The name also refers to one of the plant’s common growth habits—that of an ivy-like trailing vine.

From a scientific perspective, the comparison with ivy is misleading, as poison ivy is not an ivy at all. True ivies are in the genus Hedera in the plant family Araliaceae, which also includes ginseng. Poison ivy is in the family Anacardiaceae, which includes sumacs, mangos, pistachios, and cashews. Many members of this family, like poison ivy, contain an oily substance known as urushiol, which can provoke allergic skin reactions in many people. Two of poison ivy’s closest relatives are poison oak, Toxicodendron diversilobum, and poison sumac, Toxicodendron vernix, both of which contain urushiol and cause adverse skin reactions.

Did you know? In 1609, English Captain John Smith, known for his association with Jamestown and Pocahontas, noted the presence of a plant found in the New World that was similar in appearance to English ivy, but that caused redness, itching, and blisters.

As many of us already know, people and poison ivy are not a good combination. After making contact with this plant, most people (85%) will have an allergic response in the form of itchy contact dermatitis (skin rash). This reaction is caused by the plant’s release of an oily substance known as urushiol, which is absorbed by the skin and provokes redness and blistering within 12–48 hours. The severity of the reaction depends both on the size of skin area exposed to urushiol and an individual’s sensitivity to the substance.

Did you know? Global climate change is stimulating poison ivy to grow better and is increasing the allergenic properties of urushiol. The rise of carbon dioxide in our atmosphere is enabling poison ivy to grow about 149% faster than normal and rising global temperatures are increasing the fluidity of urushiol, allowing it to be more readily absorbed by human skin. Learn more 

From the human perspective, poison ivy might appear to lack any redeeming qualities. At best, it seems like a useless irritant and at worst, a danger to human health. However, we humans are almost unique in our sensitivity to this plant. Many other animals, such as white-tailed deer, eastern cottontails, muskrats, and a variety of insects rely on poison ivy leaves as a food source. Birds, raccoons, and fruit-eating animals feed on the plant's small white fruits and then distribute the poison ivy seeds to new habitats.

Did you know? Burning poison ivy is dangerous! Never burn poison ivy, as it will release urushiol into the smoke and allow it to be carried in air. When urushiol is inhaled it can cause a severe, life-threatening allergic response.