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Poison Ivy – A super plant we love to hate

Leaves of three, let it be.
A Yellow-rumped Warbler eating poison ivy berries in winter. Photo courtesy of Jim McCormac.

I have had no less than three formerly allergy-free friends lament about poison ivy rashes this summer. One had never gotten it even after 16 years of gardening on Nantucket. Another, a researcher with UMASS Boston, has been able to avoid rashes for 20 years until now. Is this pure coincidence or is there some reason PI rashes are on the rise?

First, let’s start with the basics. Poison Ivy, Toxicodendron radicans, is a much UN-loved species. Just reading about it right now you may be feeling itchy. While 85 % of Americans are allergic to poison ivy (PI), they’re actually allergic to urushiol, the rash-causing oil in poison ivy. Here is an amazing animated video explaining how PI allergies affect your skin. It also helps explain why some people suddenly become allergic that never were before. Poison ivy is in the same family of plants (Anacardiaceae) as mango and cashew. People who are extremely allergic to poison ivy may also be sensitive to those foods.

Although poison ivy has a bad reputation among humans, it is a native plant to Nantucket whose berries provide a valuable source of food for wildlife. The small, white berries are favorites for birds of all kinds. Deer, dogs, and other Nantucket fauna are not allergic to urushiol oil. Deer eat the berries and browse on the twigs and leaves!

Even people who are familiar with Poison Ivy marvel at the wonders that are PI on Nantucket. The climate and conditions are just right for this “shape-shifting” plant. I have been known to admire poison ivy for its ability to disguise itself as other, nearby plants. It can be seen as a small, herbaceous plant, a woody vine, and a small shrub. In the saltmarshes on Nantucket I have even seen poison ivy “trees”.  As a climbing vine, I’ve seen PI spread out its leaves to resemble the tupelo or sassafras of the trunk it’s climbing. Other times, the small PI vine can look like a thorn-less blackberry creeping along the ground.

While I hate to admit it, there are more reasons to admire the PI plant. In addition to being a master of disguise, poison ivy may be the super plant of the future. Researchers have found that PI responds extremely well to elevated CO2 levels predicted with future climate change scenarios. You think that would be the case for all  plants with more CO2, but, in a recent study, poison ivy was shown to be more adept at reacting quickly to excess CO2 growing 149 percent faster than PI grown in control plots (without elevated CO2). These elevated carbon dioxide levels are creating bigger, stronger poison ivy plants that produce more urushiol. The urushiol isn't just more plentiful, it was also more potent.

"Initial data suggests that there may be a more [powerful] form of urushiol being produced with increasing carbon dioxide," says Lewis Ziska, PhD, a weed ecologist at the U.S. Department of Agriculture in Beltsville, Md., and a co-researcher of two studies looking at poison ivy and elevated CO2 levels.

Looks like we all have one more reason to fret about climate change. At least the birds will be happy.

How to identify Poison Ivy:

  • The old adage “leaves of three, let it be,” is true. While there are other plants on island with three compound leaves (see the photo to the right), when in doubt just don’t touch it.
  • For distinguishing the woody vine on tree trunks, the hairy aerial rootlets are a telltale sign and distinct from other climbing vines. This can also be helpful in the winter.
  • This website has some great info on identification and seasonal differences you may see in Poison Ivy.  

Some tips for washing yourself up after getting into some PI:

  • Before the urushiol has been absorbed by the skin, it can be removed with soap and water. However, time is of the essence, as 50% of the urushiol can be absorbed within 10 minutes.
  • Use a good soap. This can be an ivy-specific soap like techno or just something that cuts grease. We sometimes use Dawn in our house.
  • Make sure to scrub/rub with the soap. This should be for about 1 minute without additional water.
  • Rinse thoroughly. The hotter the water the better. Think about bacon grease and how much you need to scrub and wash before it’s off your hands.