Rhus, a genus of vines and shrubs of the family Anacardiaceae, many of which are poisonous. Some species contain urushiol, a highly allergenic oleoresin mixture, and contact with them produces a severe dermatitis (rhus dermatitis) in sensitive persons. The most important toxic species are Rhus radicans L. (poison ivy), R. diversiloba L. (western poison oak), R. quercifolia (eastern poison oak), and R. vernix L. (poison sumac).
