Aliso and Wood Cyns. Wilderness Park, Laguna Niguel, CA 4-18-09. © Joan Avise

Western Poison Oak

Toxicodendron diversilobum

Distribution in Southern California

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Santiago Oaks Regional Park, Orange, CA 7-3-11. © Joan Avise

Laguna Coast Wilderness Park, Laguna Beach, CA 6-13-09. © Joan Avise

Gypsum Cyn., 3-27-11. © Ron Vanderhoff.

Unnamed Cyn, .75 mi W Sitton Peak, 11-3-11. © Ron Vanderhoff.

Peter's Cyn Wilderness Park, Irvine, CA 3-09-08. © Joan Avise

Santa Rosa Plateau Ecol. Reserve, Murrieta, Riverside Co., CA 3-01-09. © Joan Avise

Santa Rosa Plateau Ecol. Reserve, Murrieta, Riverside Co., CA 3-01-09. © Joan Avise

Compound leaves of Rhus aromatica (left) are 3-lobed, resembling Poison Oak, Toxicodendron diversilobum (right), but the middle leaflet lacks a distinct petiole (stalk) which poison oak always has. Leaves are not glossy like poison oak, and stems are downy compared to poison oak's which are hairless.  Crushed leaves have a pungent odor while poison oak is odorless. Upper Trabuco Cyn., Trabuco Trail, 7-4-12. © Ron Vanderhoff.

Galls on leaf. San Mateo Creek, San Clemente, 10-13-11. © Ron Vanderhoff.

Virus on leaf. Old Trabuco Trail, 7-24-11. © Ron Vanderhoff.

Blackstar Cyn, 10-31-10. © Ron Vanderhoff.

Top of World Sch to Dripping Cave, 2-27-11. © Ron Vanderhoff.