Leaves of Three

Facts About Poison Ivy that You Probably Don't Know

poison ivy

Poison ivy: "Leaves of three, let it be."

Poison Ivy. Leaflets of three let it be. Anyone who wanders about the woods of South Florida — or pretty much anywhere in North America — probably knows that little saying.

We’re familiar with poison ivy as a pest, a plant to be avoided at all cost because of the skin-irritating oil, urushiol, contained in its leaves and stems. Touch it and you’ll likely break out in rash, maybe even painful blisters or worse if you’re allergic to it. You might have heard of various stories of people eating the leaves in order to develop immunity to it. Not a good idea.

But there’s more to poison ivy that you probably don’t know:

— Humans and a few other primates are the only creatures on the planet susceptible to the itchy effects of poison ivy and urushiol. Deer and bears eat the leaves and stems; some 67 species of birds eat its berries. In fact, poison ivy is an important source of food for birds that winter over up north. Your dog or cat can wander through the woods with impunity, but if you give Fido a good belly rub after he’s been through a patch of poison ivy, the urushiol will come off on your hands.

— Captain John Smith of Jamestown and Pocahontas fame coined the name, poison ivy. Smith also gave us opossum.

Said Smith: "The poisoned weed is much in shape like our English ivy, but being touched, causeth redness, itching, and lastly, blisters, and which, howsoever after a while pass away of them-selves, without further harm; yet because for the time they are somewhat painfill, it hath got itself an ill name, although questionless of no ill nature.”

— Minnesota has declared poison ivy to be a prohibited noxious weed. No kidding.

poisonwood tree trunk
Poison ivy's tall, tropical cousin, the poisonwood tree, photographed at Crane Point, Key Largo.

— Urushiol comes from a Japanese word meaning lacquer. When workers restored the gold leaf on Kinkaku-ji (Temple of the Golden Pavilion) in Kyoto in 1987, they used urushiol lacquer to preserve and maintain the gold. Yes, any thieves would have been caught red-handed.

— During the occupation of Japan after World War II, American soldiers developed rashes in some rather unusual places from toilet seats (and other furniture) coated with Japanese lacquer probably made from one of poison ivy’s urushiol-containing cousins. (Poison ivy is native to Japan, the Kurile Islands, Sakhalin, Russia, Taiwan and parts of China).

— What grows in Florida and most of North America Texas eastward is called eastern poison ivy (also spelled poison-ivy). There is a western poison ivy, Toxicodendron rydbergii, found over much of the continent, including the Mid-Atlantic states and the Northeast. But not here in Florida. Thankfully.

— There are nine subspecies of poison ivy. The variety found in Florida is called T. radicans radicans.

— Poison ivy truly has become a cosmopolitan plant thanks to us humans. It’s found naturally throughout North America, Central America, the Caribbean and parts of far eastern Asia as mentioned above. Believe it or not, it’s been exported to Europe, Africa, Australia and New Zealand as an ornamental. Really.

Poison ivy is a member of Anacardiacae, the sumac family, which includes mangoes, cashews and pistachios as well as poisonwood, poison oak and poison sumac. The last three contain copiuos amounts of urushiol. Only poisonwood, aka Metopium toxiferum, however, is found in South Florida, and it’s blotchy trunk, marked with black resin, makes it easy to ID. Do not touch.

Another problematic member of the family found in South Florida: Brazilian pepper. It’s not as likely to give you a rash, but it’s one of the worst invasive plants unleashed in the Sunshine State.

— David Sedore

Published by Wild South Florida, PO Box 7241, Delray Beach, FL 33482.
Photographs by David Sedore. Photographs are property of the publishers and may not be used without permission.