The Original Mystery Plant

Photo by John Nelson

Dr. John Nelson

This vine is recognized by its compound, trifoliolate leaves and should leave alone because it is poisonous.

Depending on one's susceptibility, it can cause severe contact dermatitis. Because its foliage is unremarkable, it tends to blend into the background and sometimes becomes invisible. If a person comes in contact with it, they will probably need calamine lotion but will say that he or she never saw the vines that caused the itch.

This plant is a perfectly good native resident of eastern North America. It is at home in a variety of woodland ecosystems and does well in shade. It is common on low ground, abounding in coastal swamps, but may also be found widespread in the mountains. It is a vine and under the right conditions will climb high into the canopy.

Large vines are commonly seen attached to tree trunks exhibiting plenty of aerial roots and clinging to the tree's bark. Its branches frequently emerge at right angles and usually to the main stem.

It is not always found climbing on trees and may form bushes or scramble and run on the ground. This species is fully capable of growing in less than woodsy settings and does well in back yards.

Potentially serious rashes may result from contact with any part of the plant, which includes the vines in the winter, when no leaves are showing.

However, not everybody will end up with a rash after touching this plant. The foliage is quite pretty. The plants produce small, yellow flowers, which eventually form hard, whitish berries that many birds love to eat.

Maybe one day a horticulturist will develop a non- toxic variety to grow in gardens. In the meantime, everyone should learn to recognize this plant, and how to distinguish it from the various other non- toxic species that resemble it because there are several. The best way to avoid problems with it is to avoid all contact.

Answer to this week's mystery plant

[Answer: "Poison ivy," Toxicodendron radicans]

Dr. John Nelson is the curator of the USC Herbarium.

To learn more about the Herbarium, call 777-8196. The

department also offers free plant identification.

www.herbarium.org