Red autumn leaf of poison ivy
“Three pieces of paper, let it be” is the identity cue and warning that naturalists, foresters, rangers, botanists, teachers and gardeners use when pointing out the woody ivy poison ivy. Captain John Smith coined the term “poison ivy” in 1609 because the ivy reminded him of the English ivy in his homeland.
Poison ivy, Toxicodendron radicans, a member of the cashew family, is native to North America and grows in a wide variety of communities, from open spaces to woodlands and in disturbed areas along roads, railroad tracks, and in ditches. One of the best local places to observe the vigorous, perennial deciduous vine is Congaree National Park, where 25 percent of the trees exhibit the vine.
The plant has different growth patterns depending on where it grows and the conditions under which it is grown: shrub, semi-shrub and vine. Poison sumac reproduces sexually by seeds dispersed by birds and mammals and vegetatively by above-ground vines, rhizomes and root crowns.
The cashew family includes poison ivy, poison sumac, smoke tree, poison oak, Peruvian peppercorn, cashew nut, and mango. Each member of the family contains urushiol, a plant oil found in leaves, hairs, stems, roots, and berries. When our skin comes into contact with the oil, 80 percent of people are allergic to it and develop contact dermatitis, a red, itchy rash followed by blisters. According to the American Skin Association, as many as 50 million Americans have an allergic reaction to poison ivy each year. People at highest risk are outdoor workers in construction, forestry, grounds maintenance, landscaping, agriculture, and firefighting. Hikers, campers, dog owners, and gardeners should also be vigilant about their chlorophyll environment.
Because the oil can contaminate gloves, tools, and clothing, gardeners should wash these items after coming into contact with poison ivy. Pets that come into contact with the plant should also be washed. Dogs and cats do not get the rash, but we can get it from petting them.
If your skin comes into contact with poison ivy, wash your skin with cold water. Tecnu is a product you can use because it bonds to your skin cells before urushoil has a chance to do so.
Leaflets three, let it be so.
Urushiol is a compound that remains reactive for a long time. Dr. Susan Pell, director of the US Botanic Garden and a researcher of the cashew family, has found that urushoil remains active and can cause allergic reactions in 100-year-old herbarium specimens of poison ivy. Scientists speculate that urushoil evolved as an antimicrobial defense to protect the plant from disease and fungal, bacterial and viral attacks.
Although poison ivy is a pest to humans, it is a valuable resource for wildlife. In the spring, insects transfer pollen from the male flowers to the female flowers. In the fall, the white, waxy berries are food for autumn-migrating songbirds, and in the winter, resident birds eat the berries when other food sources are scarce. Many birds feed on insects hidden in the vines. Black bears, deer, woodrats, squirrels, rabbits, and raccoons forage on the stems and leaves of poison ivy.
For more information about poison ivy in the garden, read the Clemson Home and Garden Information Center Fact Sheet hgic.clemson.edu/factsheet/poison-ivy/.
