Map of life expectancy at birth from Global Education Project.

Sunday, July 26, 2009

Toxicodendron radicans

You may have learned that poison ivy is in the genus Rhus, but evidently the International Society of Poison Ivy Genusologists has decided that it should now be assigned to the genus Toxicodendron. Whatever. In Windham County, I would venture to guess it's the most common leafy plant. Turn around for five minutes, and it's winding around your downspouts. Through my awesome powers of googling I have learned some curious facts about this exquisite ornamental. (And yes, some fools took it over to England to plant in gardens.)

It turns out that the only species in North America to which T. radicans is toxic -- technically outrageously allergenic -- is H. sapiens. Bears and deer actually munch on it, and its fruits are a favorite of many birds -- happily for poison ivy since the birds go on to deposit the seeds in a nice, nourishing blob of guano, which is why the stuff keeps showing up where it isn't invited. You might conclude that this makes evolutionary sense since one would expect that humans are also the only species which has the cognitive chops to associate T. radicans with the highly unpleasant contact dermatitis that, for many people, follows looking at it sideways, since it takes anywhere from several hours to a couple of days for the rash to emerge.

But I would say that's too pat. There really isn't much evident advantage to the plant in being repulsive to humans. It's hard to believe the native Americans would have been uprooting large quantities of it for the soup pot if it weren't poisonous, and they would probably do the plant as much good as birds as berry pickers and seed shitters. I suspect that the plant gains some other advantage from the allergenic oil, called urushiol, and that our sensitivity to it is just happenstance.

I am very happy to say that my own sensitivity has greatly declined with age. I can now operate the weed whacker with only mild consequences, but as a youth, the dread PI was the bane of my existence. Any of my college classmates who happen to read this may recall the notorious wine party in the woods, when someone in an impaired state evidently threw a goodly sample of T. radicans on the fire. I was personally out of commission for a week -- got to skip a midterm in fact -- but some of my friends had it much worse. One guy, an organist, was diagnosed with third degree burns on his hands and had to do physical therapy to get the range of motion back in his fingers. He couldn't play for months. One of my roommates had the misfortune to take an ill-timed leak, and spent three days in bed fanning his parts.

Poison ivy exposure is a leading reason for workers' compensation claims among forestry workers and firefighters, believe it or not. Other than that it's not much of a public health concern. It hardly ever kills people, although that doesn't mean never. Fatal allergic reactions are possible. Generally it's just one of the more miserable experiences available to us, and then it goes away. I recommend a solution of zinc acetate and benzyl alcohol, sold as Ivy Dry. A tree feller of my acquaintance swears by washing yourself with gasoline as post-exposure prophylaxis. You know what, if it works, it's probably worth it.

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