Poison Oak
Toxicodendron diversilobum
Poison oak’s appearance is quite variable: it can form a spreading shrub, a dense thicket reaching ½ to 4 m in height, or a treelike vine, which can reach up to 9 m height and over 30 m long depending on growing conditions. The poisonous 3-part leaves, however, are distinct. The scalloped leaves are divided into three leaflets, 3.5 to 10 cm in length. They resemble a valley oak’s leaves, though slightly less lobed and glossier (because of the oils). The leaves change color dramatically over the course of the year: they are bronze when first unfolding in late winter, bright green in the spring, yellow-green to reddish in the summer, and bright red or pink in late summer and fall. The inconspicuous white flowers form small clusters of white to green berries.
Basic Information
Member of the sumac family, Anacardiaceae
Shrub or woody vine
One of the most common California shrubs
Winter deciduous
Habitat
Native to western North America from Washington south to Baja California, and east to Arizona
In California, this plant grows throughout the coastal and coast mountain ranges, the Transverse mountain ranges, through the Sierra foothills, and into the Sacramento Valley.
Found in a wide variety of habitats, including chaparral, open woodlands, and stream banks
Ecological Role
Black-tailed deer, mule deer, California ground squirrels, western gray squirrels, and other fauna feed on the leaves of the plant, which are rich in phosphorus, calcium, and sulfur
Birds eat the berries and utilize the plant for shelter
The vining form of this plant can climb over shrubs and up tree trucks, sometimes killing the support plant in the process by smothering or breaking it
Reproduction
Blooms from March to May
Spreads by underground rhizome (a horizontal root) or seed
Alternative Names
Pacific poison oak, western poison oak
Historical Uses
The flexible stems and shoot of this plant were used to make basketry by tribes including the Ohlone and Mendocino Indians
The sap was used to cure ringworm and warts by the Yuki, Mendocino Indians, and other tribes
The juice or soot was widely used as a black dye
Used to dye basketry, darken skin, and create tattoos
The Pomo used the soot to darken the skin of children fathered by white men in order to make them look more ‘indian’
Some native peoples, such as the Mahuna and Tolowa, consumed the leaves and buds of this plant to prevent further poisoning
The plant was also used to treat rattlesnake bites
Additional Information
WARNING: do not touch this plant! The entire plant is covered in the oil urushiol, which causes your skin to become covered in itchy bumps. Some people are not allergic to this oil, but it is not worth the risk.
Native animals, horses, livestock, and canine pets do not react to this plant’s volatile oils
