Toxicodendron Diversilobum - Appearance

Appearance

Western poison oak is extremely variable in growth habit and leaf appearance. It grows as a dense shrub in open sunlight, a tree with an 8–20 cm (3.1–7.9 in) trunk under conditions with ample sunlight, very wet winter/spring and dry summer, or as a climbing vine in shaded areas. Like poison-ivy, it reproduces by creeping rootstocks or by seeds. The leaves are divided into three (rarely 5, 7, or 9) leaflets, 3.5 to 10 centimetres (1.4 to 3.9 in) long, with scalloped, toothed, or lobed edges — generally resembling the leaves of a true oak, though the western poison oak leaves will tend to be more glossy. Leaves are typically bronze when first unfolding, bright green in the spring, yellow-green to reddish in the summer, and bright red or pink in the fall. White flowers form in the spring and, if fertilized, develop into greenish-white or tan berries. T. diversilobum is winter deciduous, so that after cold weather sets in, the stems are leafless and bear only the occasional cluster of berries. Without leaves, poison oak stems may sometimes be identified by occasional black marks where its milky sap may have oozed and dried.

Botanist John Howell observed Toxicodendron diversilobum's toxicity 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."

If one is unsure of whether one has encountered poison oak or not, an old adage states, "Leaves of three, leave them be. Leaves of four, eat some more."

• Green phase

• Flowering

• Red phase

• Berries

• Pacific Poison-oak

• Ground variation

• Climbing variation