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Summer 2010

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

Poison Ivy; Toxicodendron radicans

August 3, 2010

Poison ivy’s toxic mnemonics

While most people who work and play outdoors recognize poison ivy, they often use a variety of colorful rhymes to to help others remember what the plant looks like.

“Leaves of three, let it be”

Waxy green compound leaves have three leaflets. Brushing up against them can cause the release of a lacquer-like substance called urushiol, which can create an allergic reaction on human skin: redness, itching, blisters.


Sources: Steve Brill; Weed Science; Proceedings of the National Academy of Sciences.

“Berries of white, run in fright”

As summer unfolds, the round, green fruits of poison ivy slowly enlarge. By autumn, they will turn ripe and white -- and be just as noxious to people as the rest of the plant.

“Hairy rope, dont' be a dope”

Poison ivy exhibits several growing habits: It thrives as a ground cover from woodlands to beach dunes; it can grow into a robust bush; when it climbs trees, the woody vine, covered with wiry reddish-brown hairs, swells in diameter and sprouts arching, tree-like branches. Burning a poison ivy vine is a bad idea: Urushiol is carried in the smoke. If inhaled, it can create a life-threatening reaction in the lungs.


“Global warming, poison ivy swarming”

Poison ivy responds robustly to increasing CO2 levels, stepping up leaf and stem production -- even increasing its concentration of urushiol.

Scientists grew identical sets of poison ivy plants in atmospheres with various concentrations of carbon dioxide, based on levels from the mid-20th century, the present day and a projected future. Two-inch rhizome segments were sprouted and cultivated for 250 days before leaves were harvested and measured.

Poison Ivy growth at varying carbon dioxide levels