The Great Disguiser

By Svetlana Wasserman

Now that poison ivy is about as large as it’s going to get before shedding its leaves for the winter, it’s an ideal time to explore this multifaceted plant.

“How can you identify poison ivy?” I often ask participants on my nature walks. The most common answer I get is “shiny and reddish leaves.” Well, yes and no. Poison ivy changes shape, color, and size dramatically as it grows.

The shiny red leaves can be seen in early spring when they just emerge, and in fall as the chlorophyll drains from them.

More often the leaves are green and matte. Another indicator is the toothed edge along the leaves, which is most pronounced when the leaves are young.

Perhaps the most prolific and least recognizable form is when the plant, which is a vine, has grown thickly around a tree trunk, and to all appearances, is the tree. The rootlets that cling to the vine resemble a thick mat of fur. These mature vines can grow leaflets the size of an adult hand. Tree huggers beware!

 

 

One thing that doesn’t change is the leaf pattern. Poison ivy has compound leaves with three leaflets each. The center one is the largest, like a head with two arms outstretched below it. That is why our mantra for identifying poison ivy is, “leaves of three, leave them be.”

Since this is the plant that I get the most questions about, I am including a FAQ about poison ivy.

Q: What happens if I touch poison ivy?

A: Poison ivy contains an oil called urushiol, which about 85% of people are allergic to. Contact with urushiol causes a painful itchy rash with oozing blisters that appears about 24 to 72 hours after exposure. The rash is not contagious, so scratching won’t spread it, but will prolong the healing.

Q: I did not touch poison ivy, so why do I have a rash?

A: Urushiol can linger for a long time, so if your clothes, pets, or shoes came into contact with poison ivy, and you then touched them months later, it can transfer to your skin. Burning poison ivy releases particles of urushiol that can enter airways and affect eyes, nose and respiratory passages.

Q: What about those poor animals in the woods who come in contact with poison ivy?

A: Here’s the remarkable thing about poison ivy. The urushiol is not a poison, and animals thrive on the plant. Deer, rabbits, goats, horses devour it. A wide variety of birds survive on its berries. Even chimpanzees, who share 98% of our DNA, do not react to it. The reason that humans react so strongly to the plant lies in our own immune system. Our T-cells mistakenly identify the urushiol as a dangerous foreign threat, and they launch a full defense. The enzymes and proteins that are released by the T-cells destroy everything in the vicinity of the urushiol, and that is what causes the itchy blisters. Just as our immune systems vary from person to person and over time with regard to mosquito bites or pollen, so do our reactions to poison ivy.

Q: Should I pull out the poison ivy in my yard?

A: Unless you are concerned about children or pets getting into the poison ivy, you are best to leave it be. Most exposures occur when people are trying to get rid of the plant. Removing the plant also takes away an important food source for local wildlife. I find it is much easier to learn how to identify the plant and avoid it than to wage war against it.