I still remember the moment in my childhood in which I lost all faith in the innocent purity of plants. One day, I was a carefree adolescent at summer camp, exploring the leafy woods with my fellow campers. A couple of days later, I was an illustration for a medical textbook. “The worst case of poison ivy I’ve ever seen!” the camp nurse told the other staffers as she trotted me and my dime-sized blisters around for inspection.
OK, I kind of enjoyed the attention. The slightly awestruck reaction. What 12-year-old girl wouldn’t? But the itching, the oozing, the angry red swelling of feet and legs? Hated every minute. And since that summer, I’ve never entered forested land without conducting a slightly neurotic survey of the plant life furling about my feet.
It’s a story that places me among the countless Americans ― health officials estimate there are more than 350,000 new cases every year ― who’ve tangled with poison ivy or its relatives, poison oak and poison sumac, and regretted it. I may, however, be one of the few ivy victims who have come to admire the enemy. In fact ― have I spent too much time in the woods recently? ― my purpose here as summer begins is to defend and even praise the fascinating, sometimes beautiful and environmentally essential poison ivy plant.
The triumvirate of poison oak, poison ivy and poison sumac has been admirably holding its own against humans for centuries. Poison ivy acquired its unaffectionate label from one of the 17th-century British explorers, Capt. John Smith. A founder of early English settlements in Virginia, Smith is probably best remembered for his story of being rescued from unfriendly Indians by a young tribe member named Pocahontas. He apparently fared less well with the native plants, writing in his journal about one that upon “being touched causeth rednesse, itchynge, and lastly, blisters.” He named it poison ivy, after its resemblance to the ornamental ivies of his home country.
And poison oak and ivy ― if one can manage objectivity ― really are ornamental and startlingly pretty, especially when they unfurl crimson leaves in the spring or blaze into fiery copper in autumn. In fact ― and this is confirmed by the website at Monticello ― President Thomas Jefferson once ordered poison ivy as a decorative vine for the garden of his beloved Virginia home.
The plants are usually referred to as three-leafed, as in “leaves of three, let it be.” But they are actually more complex in design than the rhyme suggests. Each leaf is a cluster of three leaflets; the slightly glossy trios alternate from one side to the other along the stems, giving the plants a rather lacy appearance. They are astonishingly adaptable in their ability to conform to the environment, growing up trees as a flowering vine, branching out into small shrubs and creeping along as ground cover. They thrive in field and forest, in newly plowed subdivisions, along the crumbly asphalt of road edges and even on sand dunes, where they are sometimes used for erosion control.
Poison ivy’s geographic range also reflects a remarkably easygoing acceptance of living arrangements ― “Eastern” poison ivy is now found through most of the Southeast, between Arizona and Florida along the southern rim of the United States, to Nebraska and Canada in the north. If not for the western mountain ranges, notably the Sierra and the Cascades, botanists believe, it would now be flourishing along the West Coast. But really, why bother, when its close cousins, poison oak and sumac, do the job so well there?
The plants’ ability to be everywhere makes them a dependable meal for species ranging from insects to deer. Poison ivy vines produce tiny greenish-white flowers and silvery winter berries. Wild bees feed on poison ivy flowers, and no, the honey is not toxic. Wild birds depend on those waxy berries in the winter ― among the varieties known to feed on them are woodpeckers and warblers, wrens and robins, blue birds, sapsuckers and, I mention this one because I love the name, the tufted titmouse.
So it’s good news for the birds and bees, if not the rest of us, that poison ivy and its relatives brilliantly adapt to climate differences. Is it also good news that they seem to adapt, or even thrive, in response to climate change? Even I, author of this ode to Toxicodendrons (Latin name, showing off) didn’t exactly cheer when U.S. Department of Agriculture scientists announced recently that this plant species responds happily to rising levels of carbon dioxide in the atmosphere. They warned, in fact, that today’s poison ivy plant shows signs of growing 50 percent larger than the version found in the early 20th century.
Some studies also suggest that the oily sap that flows through these plants, called urushiol, might also become more toxic in a climate-changed world. Scientists already estimate that 70 percent to 85 percent of all people react badly to urushiol, accounting for those thousands of blistering inflammations reported every year.
Most biologists believe that urushiol’s unfriendly chemistry developed as a way for the plants to discourage snacking by animals. And that, of course, hungry animals, dependent on the food source, made their own adjustments in turn. We, a species that only comes in casual contact with poison ivy, would have no real biological pressure to adapt to its defenses. It turns out that occasional annoyance doesn’t drive adaptation, which is why humans are still stuck with those “rednesse” and “itchynge” issues.
So consider the steadfast poison ivy plant. It has responded to centuries of human enmity by expanding its range and increasing its annoyance potential. It serves a wide range of other species while remaining impervious to our outrage. How can you not admire such a capable life form, such an able combatant? Still, should it go further, turning into a climate-driven super-toxic ivy, you may well find me expressing my admiration for its adaptability from the safety of the great indoors.
Deborah Blum, a Pulitzer Prize-winning science writer, is the author of “The Poisoner’s Handbook: Murder and the Birth of Forensic Medicine in Jazz Age New York.” ― Ed.
