Garden tip: Watch out for poison oak

Poison oak, Toxicodendron diversilobum, is flaming red in the fall landscape. However, don’t gather them for any bouquets to decorate your table. All parts of the plant are poisonous, causing painful dermatitis.

Many people in the eastern United States are familiar with poison ivy, Toxicodendron radicans. The same oil, urushiol, causes the annoying skin rash in both.

The old adage, “Leaves of three, leave it be,” can help identify poison oak or ivy. Poison oak is variable in size and structure. For example, the leaves may be as large as a dinner plate in wet years.

The National Park Service has written about Chumash medicinal plants. It is believed that these Native Americans used juice from poison oak to treat warts, cankers and skin cancer.

— Katie Martin, UC Marin Master Gardeners