Pacific poison oak

Toxicodendron diversilobum

''Toxicodendron diversilobum'', commonly named Pacific poison oak or western poison oak , is a woody vine or shrub in the Anacardiaceae family. It is widely distributed in western North America, inhabiting conifer and mixed broadleaf forests, woodlands, grasslands, and chaparral biomes. It is known for causing itching and allergic rashes in many humans, after contact by touch or smoke inhalation.
poison oak The hills in this area were *covered* in this stuff.... we had to watch carefully to not touch any, but we managed! Geotagged,Pacific poison oak,Spring,Toxicodendron diversilobum,United States


''T. diversilobum'' is extremely variable in growth habit and leaf appearance. It grows as a dense 0.5–4 m tall shrub in open sunlight, a treelike vine 10–30 feet and may be more than 100 feet long with an 8–20 cm trunk, as dense thickets in shaded areas, or any form in between It reproduces by spreading rhizomes and by seeds.

The plant is winter deciduous, so that after cold weather sets in, the stems are leafless and bear only the occasional cluster of berries. Without leaves the stems may sometimes be identified by occasional black marks where its milky sap may have oozed and dried.

The leaves are divided into three leaflets, 3.5 to 10 centimetres long, with scalloped, toothed, or lobed edges. They generally resemble the lobed leaves of a true oak, though tend to be more glossy. Leaves are typically bronze when first unfolding in February to March, bright green in the spring, yellow-green to reddish in the summer, and bright red or pink from late July to October.

White flowers form in the spring, from March to June. If they are fertilized, they develop into greenish-white or tan berries.

Botanist John Howell observed the toxicity of ''T. diversilobum'' obscures its merits:
─⟶ "In spring, the ivory flowers bloom on the sunny hill or in sheltered glade, in summer its fine green leaves contrast refreshingly with dried and tawny grassland, in autumn its colors flame more brilliantly than in any other native, but one great fault, its poisonous juice, nullifies its every other virtue and renders this beautiful shrub the most disparaged of all within our region."
TOXICODENDRON DIVERSILBUM. Pacific Poison Oak. Geotagged,Pacific poison oak,Plant,Spring,Toxicodendron diversilobum,United States


''T. diversilobum'' is found in California , the Baja California peninsula, Nevada, Oregon, Washington, and British Columbia. The related ''T. pubescens'' is native to the Southeastern United States. ''T. diversilobum'' and ''T. rydbergii'' hybridize in the Columbia River Gorge area.

''T. diversilobum'' is common in various habitats, from mesic riparian zones to xeric chaparral. It thrives in shady and dappled light through full and direct sunlight conditions, at elevations below 5,000 feet . The vining form can climb up large shrub and tree trunks into their canopies. Sometimes it kills the support plant by smothering or breaking it.

The plant often occurs in chaparral and woodlands, coastal sage scrub, grasslands, and oak woodlands; and Douglas-fir , hemlock–Sitka spruce, ''Sequoia sempervirens '', ''Pinus ponderosa'' , and mixed evergreen forests.


Black-tailed deer, mule deer, California ground squirrels, western gray squirrels, and other indigenous fauna feed on the leaves of the plant. It is rich in phosphorus, calcium, and sulfur. Bird species use the berries for food, and utilize the plant structure for shelter. Neither native animals, nor horses, livestock, or canine pets demonstrate reactions to urushiol.

Due to human allergic reactions, ''T. diversilobum ''is usually eradicated from gardens and public landscaped areas. It can be a weed in agricultural fields, orchards, and vineyards. It is usually removed by pruning, herbicides, digging out, or a combination.


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SpeciesT. diversilobum