Steven Foster – “You know what that bundle of plants in your arms is called?” I asked a t-shirt clad young man who was clearing brush next to the Eureka Springs Independent office. “It’s poison ivy,” I said.
“You’re kidding,” he replied. “Nope, poison ivy,” I confirmed.
To me, the surprise was that here was a local kid, who grew-up hunting, fishing and camping, yet he didn’t know what poison ivy looks like.
Poison ivy is called Toxicodendron radicans (formerly known as Rhus radicans). Here in the Ozarks we have poison ivy, as well as a variant sometimes called poison oak (Toxicodendron pubescens, T. toxicarium, Rhus toxicodendron, Plantus infinitconfusesus). Really, you probably don’t want to get close enough to the two to discern the difference. The names “poison ivy” and “poison oak” are used indiscriminately to refer to the infinite variation in size, leaf shape, teeth shape, hairiness, and habit varying from ground creeper to thinly-disguised upright shrub to climbing liana that can reach 150 ft. up into a tall tree. Give it an opportunity, and it will grow. In Arkansas we do not have poison sumac (Toxicodendron vernix).
The genus Toxicodendron is comprised by about 20 species in the cashew family (Anacardiaceae) found in North America and eastern Asia. In fact, our common poison ivy is the most widespread species in the entire family occurring throughout eastern North America as well as Japan and China. It is highly variable, further divided by botanists into nine subspecies.
It was given the name poison ivy in the early 1600s by Captain John Smith (1580-1631) of Jamestown, Virginia, fame who observed that it differed little in appearance from English “yvie,” and stated that it “causeth rednesse, itchynge, and finally blysters,” but goes away on its own.
Highly variable in form and habit, poison ivy is the best known of all poisonous plants in North America. Fifty percent of the population is allergic to the plant, which causes, painful, irritating contact dermatitis. All plant parts (especially the sap) contain irritant, non-volatile, phenolic substances referred to as urushiol or toxicodendrol. Found in resin canals, the oily mixture is released when the plant is bruised, even slightly. The toxins can bind to skin proteins, resulting in the typical reaction many people experience.
The Ozarks is at the center of genetic evolutionary diversity for poison ivy, which from a practical standpoint means that endless variation is inevitable. Get to know poison ivy in all its variation. No two plants look exactly alike.