Poison oak and poison ivy do not come in only one specific form, as these plants can be shrubs, ground cover or vines. This makes it very difficult to identify these plants with any certainty, despite the old proverb "Leaves of three, let it be," which pertained to the typical arrangement of their leaves. To identify them, look at the different features and aspects of these plants, which contain a substance called urushiol that precipitates serious and painful rashes in sensitive individuals.
Poison Oak Identification
Look for poison oak in the form of a woody shrub in open sunlit areas and as a climbing vine in places where there is dense shade. As a shrub, poison oak ranges from 1 to 6 feet high and can grow in dense thickets. As a vine, it will support itself on other trees and shrubs, growing much taller using aerial roots, which bind the plant to taller vegetation.
Study range maps to determine if poison oak grows where you live. Poison oak is common on the West Coast in the United States, as well as in the Southeastern section of the nation.
Search for a plant with three leaflets attached to one stalk. In some cases, poison oak can have as many as nine leaflets on a single stalk. Usually though there are three, with the stalk by which the middle leaflet attaches to the main stalk being longer than those of the other two leaflets.
Examine these leaflets closely, ascertaining their size and shape. Poison oak gets its name from the fact that it has lobed leaves that resemble those of oak trees. The surface of these leaves is often shiny and frequently the lower surface is hairy. The leaflets range from an inch to 4 inches in length.
Watch the change in color of the poison oak as time progresses. According to the University of California's Integrated Pest Management website, the leaves start out as a light green color, with some being reddish, but change to all green in the late spring and summer. By autumn, poison oak leaves turn to red and orange before falling off the plant.
Poison Ivy Identification
Look for poison ivy as a low-growing ground plant or a vine, capable of extending to the tops of trees. In vine form, its brown aerial roots will affix it tightly to the host tree. Poison ivy vines can sometimes grow to sizes as thick as your arm, states the Great Plains Nature Center website.
Observe the compound leaves of poison ivy. They exist in threes on a central stalk, with one leaflet located at the tip of the stalk and two growing opposite each other at the base of the stalk.
Study the features of poison ivy leaves. Notice that they are usually between 2 and 4 inches long and have either a dullish-green hue or a more glossy green shade to them. The leaf at the end of the stalk is normally slightly larger than the other two, but all three typically possess pointed ends.
Watch the poison ivy leaves turn a brilliant red color in the fall. Poison ivy leaves are among the first foliage to change color in the autumn, and you will frequently see them form a red "path" up the side of a tree when attached to a vine.
About this Author
John has written thousands of articles for Demand Studios, Associated Content and The Greyhound Review. A Connecticut native, John has written extensively about sports, fishing, and nature.