Plant defenses are not-so-pleasant for us humans
Like poisonous serpents, some plants developed toxic properties in order to protect themselves against predators. Besides insects, the major plant predators are herbivores: bison, deer, rabbits, mice, caterpillars, aphids and any other critters — including humans — that devour plant matter above or below ground.
Other “herbivore defenses” include spines, stinging hairs that detach in a predator’s skin like a bee’s stinger, thorns and spiny-edged leaves. Honey locust is perhaps the thorniest plant in our flora. Osage orange was used in the mid-West to fence out cattle before the invention of barbed wire.
In turn, numerous animals have evolved the ability to tolerate or detoxify plant defense compounds. Beavers, for instance, feed heavily on aspen bark or other plants that contain salicin, which negates the defense compounds devised by many of the other plants they eat. Insects and mammals generally prefer to feed upon leaves and shoots of plants, as they are tender, digestible and contain the least concentrations of the defense compounds.
The Cherokees still harvest and cook a number of mushrooms each fall. But they learned early on — no doubt by trial and error — to avoid all of the species of Amanitas, a genus that does contain some choice edible species. But Amanitas are one of those critical plant-gathering categories in which an identification mistake can mean death.
The destroying angel, a strikingly beautiful Amanita mushroom, has acquired a reputation as the deadliest member of the genus, but it’s the aptly named death cap that’s responsible for the most fatalities each year. As little as half a fresh death cap can be fatal to an adult. Children ingesting that amount have a mortality rate of 50 percent. A period of nausea and shock six to 24 hours after ingestion is followed by a four-day period of “false recover,” after which death occurs within seven to 10 days due to liver, kidney and heart failure.
We can’t discuss poisonous plants and their defenses without considering poison ivy. I used to joke about poison ivy until several years ago when I inadvertently chain-sawed a huge vine growing on a black locust tree I’d cut down for firewood. I got the juice all over myself in some very sensitive places.
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My attitude was immediately adjusted — no more poison ivy jokes. Before that incident, I was pretty much immune, but these days even a casual encounter can bring on the itching and scratching.
The culprit is urushiol, a sap-like oil found in the roots, stems, leaves, flowers and fruits of poison ivy that evolved as a chemical defense mechanism against browsing herbivores and, perhaps, insects. It’s so powerful that one part mixed with 60,000 parts olive oil is said to still cause infection.
The Cherokees either rubbed on the beaten flesh of a crawfish or applied the juice from seven blossoms of jewelweed. The early white settlers applied a poultice of crushed jewelweed stems and leaves.
Other old-time antidotes included the use of boiled milkweed, a potentially powerful concoction comprised of buttermilk and gunpowder, a mixture of vinegar and salt, and a mixture of soap and wood ashes.
Many still swear by jewelweed, but the best antidote, for me, is Dawn dish detergent. Something in that brand of detergent, which is also a degreaser, completely neutralizes the effects of urushiol on my skin.
I apply the detergent liberally to the irritated area and let it dry. After just a few minutes there’s almost immediate relief. And after an hour or so the irritation is eradicated.
Accordingly, a modern-day dish detergent has become my counter defense to another defense mechanism evolved eons ago by poison ivy.
(George Ellison is a naturalist and writer. He can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it..)
