Toxicodendron diversilobum (syn. Rhus diversiloba), commonly named Pacific poison oak or western poison oak, is a woody vine or shrub in the sumac family, Anacardiaceae. It is widely distributed in western North America, inhabiting conifer and mixed broadleaf forests, woodlands, grasslands, and chaparral biomes. Peak flowering occurs in May. Like other members of the genus Toxicodendron, T. diversilobum causes itching and allergic rashes in most people after contact by touch or smoke inhalation. Despite its name, it is not closely related to oaks. Description Toxicodendron diversilobum is extremely variable in growth habit and leaf appearance. It grows as a dense tall shrub in open sunlight, a treelike vine and may be more than long with an trunk, as dense thickets in shaded areas, or any form in between. It reproduces by spreading rhizomes and by seeds. The plant is winter deciduous, so that after cold weather sets in, the stems are leafless and bear only the occasional cluster of mature fruit. Without leaves the stems may sometimes be identified by occasional black marks where its milky sap may have oozed and dried. The leaves are divided into three (rarely 5, 7, or 9) leaflets, long, with scalloped, toothed, or lobed edges. They generally resemble the lobed leaves of a true oak, though tend to be more glossy. Leaves are typically bronze when first unfolding in February to March, bright green in the spring, yellow-green to reddish in the summer, and bright red or pink from late July to October. White flowers form in the spring, from March to June. If they are fertilized, they develop into greenish-white or tan drupes. Botanist John Howell observed that the plant's toxicity obscures its aesthetic values: In spring, the ivory flowers bloom on the sunny hill or in sheltered glade, in summer its fine green leaves contrast refreshingly with dried and tawny grassland, in autumn its colors flame more brilliantly than in any other native, but one great fault, its poisonous juice, nullifies its every other virtue and renders this beautiful shrub the most disparaged of all within our region. Distribution and habitat Toxicodendron diversilobum is found in California (Los Angeles was built on the site of a village named Yaangna or iyáanga’, meaning "poison oak place"), the Baja California Peninsula, Nevada, Oregon, Washington, and British Columbia. The related T. pubescens (eastern poison oak) is native to the Southeastern United States. T. diversilobum and