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Toxicodendron diversilobum
Also called Poison oak, Western poison oak, Pacific poisonoak
A woody shrub or climbing vine in the cashew family, native to western North America, best known for causing severe itchy rashes. It is a species, not a true oak despite its name, and is extremely variable in form, from low shrub to climbing vine.
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, nor is it a true tree.
Toxicodendron diversilobum leaves and twigs have a surface oil, urushiol, which causes an allergic reaction. It causes contact dermatitis – an immune-mediated skin inflammation – in four-fifths of humans. Most, if not all, will become sensitized over time with repeated or more concentrated exposure to urushiol.
The active components of urushiol have been determined to be unsaturated congeners of 3-heptadecylcatechol with up to three double bonds in an unbranched C17 side chain. In poison ivy, these components are unique in that they contain a -CH2CH2- group in an unbranched alkyl side chain.
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 T. rydbergii (western poison ivy) hybridize in the Columbia River Gorge area.
Asian Lacquer Tree · Atlantic poison oak · Poison ivy · Western poison ivy · Chinese Lacquer · Poison sumac · Poison oak
Text excerpted from the Wikipedia article Toxicodendron diversilobum by its contributors, under CC BY-SA 4.0; the excerpts and the care summary drawn from them are shared under the same licence.
The care summary was written by AI (Claude, Anthropic) from the sources on this page, with general growing knowledge where they are silent. Check before relying on it.
Life form, climate and native range: World Checklist of Vascular Plants, Royal Botanic Gardens, Kew (CC BY 3.0), reformatted; see Plants of the World Online.
