Pacific poison oak is a native deciduous shrub or climbing vine distributed along the western coast of North America from Baja California into British Columbia. All parts of the plant contain urushiol, an oily resin that causes allergic contact dermatitis in the majority of people who contact it. It establishes readily in chaparral, woodland edges, scrub, and disturbed sites throughout its range.
Growth form shifts with available light: plants in full sun become dense, multi-stemmed shrubs; those in shade send out long vining stems that climb trees. Leaves turn vivid red and orange in fall. Cream-colored berries persist through winter and are consumed by more than 60 bird species. Deer, squirrels, and black bear eat the leaves and fruit without reaction, giving the plant genuine ecological value in its native habitat. Root systems are deep and persistent; cut stems resprout reliably over multiple seasons.
Some California Native American peoples applied diluted preparations to warts and ringworm and used the sap as a source of permanent black dye in basketry. Burning poison oak is extremely hazardous — urushiol volatilizes in smoke and can cause severe internal pulmonary injury.