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poison ivy, poison oak, and poison sumac, woody vines and trailing or erect shrubs of the family Anacardiaceae (sumac family), native to North America. They are sometimes considered as several species of Rhus, the sumac genus, but are usually distinguished as Toxicodendron radicans (poison ivy and poison oak) and the larger T. vernix (poison sumac). The whitish berrylike fruits often persist through winter. The leaves of T. radicans are composed of three smooth leaflets. Both species have vivid red autumn foliage. Poison oak is a name generally used in the South and West for the bushy kinds.
The irritant principle, urushiol, is present in almost all parts of the plant. Direct or indirect contact (clothing, tools, or animals that have touched the plant, or smoke from burning the plants) sets off a skin eruption that may vary from simple itching inflammation to watery blisters, depending upon the sensitivity of the individual. The eruption appears within a day to two weeks depending upon sensitivity. It begins on the portion of the body that has come in contact with the plant, usually the hands, which then can spread it to the face and other areas. Washing contaminated skin as soon as possible after contact can reduce the severity of symptoms. These plants are classified in the division Magnoliophyta, class Magnoliopsida, order Sapindales, family Anacardiaceae.