POISON IVY, the name commonly given in North America to several native shrubs of the sumach genus (Rhos or Toxico dendron; family Anacardiaceae), called also poison oak, the foliage and other parts of which are more or less poisonous to the touch, producing in many persons severe inflammation of the skin. They are mostly small, much branched, somewhat climbing woody plants, with dark-green leaves, usually of three leaflets, small greenish flowers, and a whitish, berry-like (drupaceous) fruit. The common poison ivy (R. Toxicodendron), of the eastern half of the United States and adjacent Canada, is usually low and bushy, scrambling over small shrubs, fences and walls, but in woods sometimes ascending trees. The three ovate, pointed, usually smooth leaflets are entire or few toothed. This plant is often popularly confused with the harmless Virginia creeper (q.v.), which has larger leaves composed of five leaflets.
The poison oak (R. quercifolia), of the Southern States, is an erect shrub, I to 2 ft., with the leaflets conspicuously five- to seven-lobed. The western poison
oak (R. diversiloba), in Cali fornia, usually an erect shrub, 3 to 9 ft. high, but some times ascending trees, has leaves of three roundish, variously lobed leaflets, suggestive of oak leaves but smaller. The poison sumach (R. Vernix) known also as poison elder, poison ash and poison dogwood, the most dan gerous species, native to swamps from Quebec to Minnesota and south to Florida and Texas, is a shrub or small tree, sometimes 25 ft. high. It differs from the foregoing in the division of the leaves, which are composed of from 7 to 13 oblong, entire leaflets.
As a preventive following ex posure, bathing the affected parts with a solution of acetate of lead, if applied within one or two hours, is said to be effective. Washing the exposed parts with soap and water or with alcohol removes the poison. Applications of the fluid extract of grindelia or of a solution of potassium permanganate have also been recommended.