Poison ivy and poison oak
Toxicodendron radicans and Toxicodendron diversilobum (previously Toxicodendron diversibba)
Cashew (Anacardiacese) Family
Description: These two plants are quite similar in appearance and will often crossbreed to make a hybrid. Both have alternate, compound leaves with three leaflets. The oil in the plants is the primary culprit and all parts, at all times of the year, can cause serious contact dermatitis. Even plants that have been dead for several years may still contain the oily irritant. About 15% to 30% of people have no adverse reaction to poison ivy or poison oak and persons who are frequently exposed to either may develop an immunity to its toxins.
Symptoms include redness, itching, oozing sores, and blistering of the skin and can last from one to four weeks. Oatmeal and baking soda can be used to ease the symptoms.
The leaves of poison ivy are smooth or serrated. Poison ivy grows as a vine along the ground or climbs by red feeder roots. It can sometimes grow as a shrub reaching heights of 1.2 meters (4 feet) tall. Poison Ivy leaves consist of three somewhat shiny, smooth, almond shaped leaflets about 3-12 centimeters (1-5 inches) long and occasionally longer. Leaflets have few or no teeth along the edges. Leaf color ranges from light green to dark green turning bright red in the fall. Leaflet clusters alternate along the vine which may have aerial rootlets that attach to climbing surfaces. Flowers are yellowish to greenish white, and grow in clusters about 3 inches above the leaflets. Fruits are berry-like, grayish white in color, and contain small seeds.
These four characteristics are sufficient to identify poison ivy:
- clusters of three leaflets
- alternate leaf arrangement
- lack of thorns
- each group of three leaflets grows on its own stem, which connects to the main vine.
There are various poems and phrases people have used to help remember poison ivy identification. Here are a few:
- “Longer middle stem; stay away from them.” This refers to the middle leaflet having a visibly longer stem than the two side leaflets
- “Leaves of three; let it be.”
- “Hairy vine, no friend of mine.”
- “Raggy rope, don’t be a dope!” Poison ivy vines on trees have a furry “raggy” appearance. This rhyme warns tree climbers to be wary. Old, mature vines on tree trunks can be quite large and long, with the recognizable leaves obscured among the higher foliage of the tree.
- “One, two, three? Don’t touch me.”
- “Berries white, run in fright” and “Berries white, danger in sight.”
- “Red leaflets in the spring, it’s a dangerous thing.” This refers to the red appearance that new leaflets sometimes have in the spring. (Note that later, in the summer, the leaflets are green, making them more difficult to distinguish from other plants, while in autumn they can be reddish-orange.)
- “Side leaflets like mittens, will itch like the dickens.” This refers to the appearance of some, but not all, poison ivy leaves, where each of the two side leaflets has a small notch that makes the leaflet look like a mitten with a “thumb.”
- “If butterflies land there, don’t put your hand there.” This refers to the fact that some butterflies land on poison ivy, since they are not affected, which provides them protection as their predators avoid eating the plant.
- “If it’s got hair, it won’t be fair.” This refers to the hair that can be on the stem and leaves of poison ivy.
Like Poison Ivy, Poison Oak may grow as a woody vine (typically in shadier areas) or more typically as a dense shrub (in more open areas). Poison oak’s leaves emerge from small stems and are divided into three leaflets (occasionally five, seven, or nine leaflets) about 1-4 inches long, that may be scalloped, toothed, or lobed and resemble oak leaves. The appearance of the leaves can vary greatly with some having softly lobed edges and others having more sharply toothed or jagged edges. Two of the leaves emerge opposite from each other with a third leaf continuing out of the stem between them. Leaves will be bright green in the spring changing to yellow-green or reddish during the summer and bright red in the winter. The greenish-white flowers are small and inconspicuous and are followed by waxy green, pumpkin shaped berries that turn waxy white or yellow, then gray. In places where the stem has been cut, the sap may ooze and leave black markings on the stem.
Habitat and Distribution: Poison ivy and oak can be found in almost any habitat in North America. It often prefers wooded areas, especially along the edges of woods. It can also grow in rocky areas and in open fields.