“Leaflets 3, let it be!” Few plants carry 3-parted compound leaves, and this is an easy way to recognize a very irritating plant. Some bean vines have 3-parted leaves, but poison ivy is woody, and attaches with aerial roots. Not related to invasive English ivy, poison ivy can grow as an erect shrub or climber. Leaves are variable – they may be stiff and leathery or thin, hairy or not, shiny or dull, toothed or not. The red or yellow fall foliage is especially conspicuous.
Twigs are brown with short aerial rootlets; old stems, covered with fibrous roots, look hairy. Small yellowish flowers blooming in May-July produce small clusters of round white fruits in August-November.
Poison ivy is found in every county in Virginia, and widely distributed throughout the eastern and central United States. A close relative with lobed leaflets of 3, poison oak (Toxicodendron pubescens), does not extend into the northern states nor Canada, but is found in several coastal plain counties and across Virginia. Unlike poison ivy, poison oak never vines – it is always an upright shrub and it tends to occur in drier, sandier habitats than does poison ivy.
Human sensitivity to the irritating oil urushiol is variable, and 15-25% of the population is not at all allergic to poison-ivy and will never develop a reaction. Some people require prolonged or repeated exposure to the plant to develop a rash, but about half of all people will break out with a single contact, some requiring hospitalization. Without the leaves, poison ivy vines are difficult to identify in the winter, and for persons with high sensitivity, touching a stem or the roots will cause an allergic reaction.
Despite poisonous effects of the plant on humans, the fruits are relished by over 60 species of birds. Many seeds are passed undamaged through their digestive systems, allowing wide distribution of this noxious vine.
By Helen Hamilton, Past-president of the John Clayton Chapter, VNPS
Photo: Poison ivy (Toxicodendron radicans) taken by Jan Newton