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Poison Ivy

poison ivy leaves
Gary Kling, University of Illinois, Bugwood.org

Poison Ivy (Toxicodendron radicans) is a native plant and one of the most hated, not only because of the itchy rash caused by the slightest contact, but also because it is so difficult to spot. The appearance of the leaves and the growth habit are so variable that even experienced outdoors people can be fooled. Poison ivy is also extremely common, and apt to grow where people are sure to encounter it.

Identification

The leaves always have three leaflets. The central end leaflet is largest and has a distinct stem. The two lower leaflets are smaller, often asymmetrical, and attach directly to the leaf stem. Leaves are usually somewhat glossy especially in sun, but not always. Leaves may have smooth margins or a few large teeth (edge looks notched). Young leaves are often reddish.

Poison ivy is a woody vine capable of climbing 75 feet or more, but often grows as a ground cover. It may also look like a shrub, or even a tree, if it has some kind of support.

Poison ivy climbs with black wiry clinging roots along the stem. It does not have tendrils and it does not twine. Old vines may be so covered with roots that look dark and hairy. A mature poison ivy vine on a tree will be a tightly clinging leafless stem as much as 3 inches in diameter growing straight up a tree trunk for several feet before it sends out flowering branches. These side branches are thin, often unbranched and may be up to 6 feet long. They come off the stem almost at right angles, and have a very characteristic appearance.

Poison ivy growing up a tree
Poison ivy growing up a tree

The leaves can be alarmingly big, sometimes 12 inches wide (an unnerving sight when encountered at head height along a trail). Clusters of small yellowish flowers are followed by small whitish berries.

Where is poison ivy located?

Poison ivy is native to North America, and present statewide in New York. It is extremely common, especially when it grows as a ground cover. Thin woody stems run along the ground and become rooted in. Leaves grow on short slender upright shoots, often mixed in with grass. Poison ivy is especially common along edges of wooded areas, paths, and meadows. It prefers rich soils, good moisture and the partial shade of forest edges, but seems to be able to grow almost anywhere except on very dry hot sites. It will however grow well on hot dry limestone outcrops.

Since it is tolerant to salt spray it is common in beach areas, often growing in low patches on dunes. It is also tolerant of road salt, and is common in ditches and on roadsides. It climbs trees, buildings, fence posts, phone poles and rock outcrops.

Poison ivy is primarily spread by birds who eat the berries.

Why is poison ivy dangerous?

All parts of the plant contain a resinous oil called urushiol (you-ROO-she-all), which is a potent allergen. Individuals differ in sensitivity. Usually a person has to be exposed at least once previously to become sensitized and develop an allergic reaction. The typical skin reaction of an intensely itchy rash appears up to 24 hours after exposure. In some people, the rash progresses to severe blistering and may require steroid treatment.

poison ivy plant hairy poison ivy vine poison ivy with red leaves poison ivy berries