Poison oak, Toxicodendron diversilobum, is one of the most widespread native shrubs in California. At the start of the Sylvan Trail, near the picnic area, you will find a particularly large stand of poison oak in several forms. It can grow low to the ground and look like a stick, form an upright bush, or twine up a tree as a tall vine. Its most recognizable feature is its lobed, oak-like leaves that grow in clusters of three.
Leaves of Three, Let it Be.
Poison oak can cause a painful, itchy rash if you touch any part of the plant, even dead leaves or bare twigs. An easy way to remember how to identify poison oak is with this rhyme, “Leaves of three, let it be. If it’s shiny, watch your hiney.”
In the spring, poison oak leaves are bright green and very shiny. Plants may have small white flowers that turn into pale green or tan berries later in the season. An oily resin called urushiol is found in the roots, stems, leaves, flowers and berries. This resin is what causes a poison oak rash in an estimated 80% to 85% of people.
In summer and early fall, the leaves turn duller green and eventually, bright red. Poison oak is deciduous, so by late fall it may have no leaves at all.
An Important Plant for Wildlife.
Poison oak is an important food source for at least 50 species of birds who feast on the berries and seeds. Deer, squirrels and woodrats also enjoy eating the leaves, stems and berries. These animals don’t develop allergic rashes the way humans do. In fact, many animals make their homes in the thickets of poison oak shrubs.
I Think I Touched It. Now What?
If you think you have touched poison oak, be very careful not to touch your face or eyes. Use hand sanitizer or an oil-removing cleanser as soon as possible and wash the area with cool water and a cleanser designed to remedy poison oak when you get home. Avoid touching clothes or shoes that might have come in contact with poison oak and be sure to wash everything thoroughly.
Check out our Field Guide and PlantID.net for more details about poison oak.