Leaves of Three

by Matt Candeias, author of In Defense of Plants

posion ivyLeaves of three, let it be… no seriously, let it be. Many of you may be all too familiar with the horrible allergy that a good portion of the population has to poison ivy, but all hate aside, this plant species is one of most valuable plants for wildlife!

Poison ivy (Toxicodendron radicans) is well known to most of us. If you are like me, then you are lucky enough not to be allergic to the compound urushiol. In fact, this plant is not poisonous at all! It is our own bodies that create the severe reaction to this chemical. When it comes into contact with exposed skin, our bodies ramp up defenses to the extreme and begin to attack the compound. Sadly, the skin suffers severe collateral damage from this friendly fire. Oddly enough, we seem to be one of the only species on this planet that is affected by urushiol. Mammals and insects feed freely on the leaves, bees go crazy over the flowers, and over 60 species of birds eat the fruit. The berries are a wonderful source of food for many migratory bird species! So why does the plant produce these compounds? The truth is, we don’t really know. Seeing as how many other species make use of this plant, it is doubtful that urushiol is a defense compound. Perhaps it is a metabolite or just a secondary chemical produced by some form of biochemical pathway. Either way, production of urushiol probably predates the emergence of humanity by a long shot. Like I said above, it is our own bodies that produce the reaction.

So, my point here is, I am sorry to all of those out there who have suffered through a bad interaction with this plant. My sympathies go out to you! However, if this plant is growing in a place where you won’t come into contact with it, consider leaving it be. Many other organisms benefit from it being there and the biological community is that much richer for it. Evidence is coming in recently that shows that this family of plants are responding quite well to increased CO2 and are even ramping up their production of urushiol. Be careful and be aware but perhaps be willing to live with it if you can!

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