Crow’s Nest: I bet you’ve never seen flowers like this. Not this close, anyway.

These lovely flowers (very close up) are from poison ivy (Toxicodendron radicans).

It is blooming right now at the preserve, and the vines are humming with the sound of various species of pollinating bees. (A quick online search suggests that honey made from poison ivy nectar has none of the reaction-causing effects of contact with the plant itself.) For why it is properly called contact dermatitis and not an allergic reaction, see Tim Burris’ 2010 blog post here.

No matter what you think of it personally, poison ivy is a native plant and a valuable wildlife plant both as a nectar source, food source for herbivorous insects, and fruit eaten by birds.

We do have a bit more of it than we’d like, and I do occasionally cut poison ivy away from places where visitors might come in contact with it. And off of trees along roads where it could be hiding the tree’s defects and prevent us from evaluating the tree’s potential hazard of falling.

In a world that has increasing levels of carbon dioxide, there will be winners and losers. Poison ivy will be a winner. A study in North Carolina suggests that it will grow faster and have more potent version of the chemical urushiol that triggers contact dermatitis in many people.

As you know poison ivy has more deeply lobed juvenile leaves than those that appear on mature plants that have climbed high up trees. Many species have different leaves on young plants or new growth, sometimes larger to allow for greater photosynthesis. But why not keep the large leaves upon maturity? I read a thorough explanation on the website of the poison ivy horticulturist, Umar Mycka. On juvenile leaves Mycka says, “The edges of [the leaflets] are toothed and terminal leaf has short neck. Toothing of leaves facilitates good water evaporation which leads to quick growth. The short neck enables conservation of plant tissue and allows for complete and coordinated movement of the three leaflets together to better determine and note the sun’s path.” The unlobed leaves of mature plants allows less evapotranspiration—slower growth but less susceptibility to drought.

Appreciate poison ivy from a distance. As we say, “leaves of three, leave them be.” I usually have a mild rash for much of the summer as I can’t avoid the plant while doing land management here.

Posted by Daniel Barringer on May 26, 2012.