Western poison oak (Toxicodendron diversiloba) is a shrub,
which can grow like a vine. It is native to the Western United States, from
British Columbia to Baja, California, from the mountains to the coast. Poison
oak is the counterpart to the East Coast poison ivy. Its leaves are pinnately
trifoliate, each leaf with multiple lobes; the greenish-white flowers grow in panicles;
and the fruit is a drupe. Leaves turn red or pinkish in fall, so they are sometimes
used in landscaping for fall color. In the San Francisco Bay Area, the plant
thrives in the redwood forest, mixed evergreen forests, oak woodland, and chaparral
plant communities, and in riparian zones. As the common name suggests, it frequently
grows near oak trees, and its leaves resemble oak leaves, especially live oaks,
such as Quercus agrifolia. Deer and livestock
browse poison oak, which contains high levels of phosphorus, sulfur and calcium.
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| Poison
oak leaves resemble oak leaves. Photo by Gary A. Monroe @ USDA-NRCS PLANTS Database (http://plants.usda.gov/java/profile?symbol=TODI&photoID=todi_007_ahp.tif). |
Poison oak causes skin irritation for most people, and can
cause serious respiratory inflammation if inhaled while burning. Some people report they have
no reaction upon first exposure, then immediate and painful reactions on subsequent
exposure. A few people report no reaction, but this seems rare.
California native people groups, such as the Ohlone, ingested small quantities of the leaves to
prevent the rash, and to prevent colds. They made baskets of the long fibers, and used the leaves to
wrap corn meal for baking in hot coals.
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