How to identify poison oak (west coast)

Pacific poison oak (*Toxicodendron diversilobum*) is the western counterpart to eastern poison ivy. It is the dominant urushiol-producing plant in California, Oregon, and Washington -- and one of the most common causes of allergic dermatitis in the western United States. An estimated 15–20 million.

Pacific poison oak (Toxicodendron diversilobum) is the western counterpart to eastern poison ivy. It is the dominant urushiol-producing plant in California, Oregon, and Washington — and one of the most common causes of allergic dermatitis in the western United States. An estimated 15–20 million Americans develop contact dermatitis from Toxicodendron plants each year, per UC IPM.

I don't garden on the West Coast, so this guide is sourced from UC IPM and USDA publications rather than personal observation.

What is Pacific poison oak?

Toxicodendron diversilobum is a native plant of the Pacific Coast and western states. Per UC IPM, it grows from British Columbia south through California and east to Arizona and Nevada. It is not found east of the Sierra Nevada/Cascades in any significant amount.

Per USDA NRCS, there is also eastern poison oak (Toxicodendron pubescens), found in sandy soils of the southeastern Atlantic coastal plain and lower Midwest — a separate species that also has lobed leaflets.