Yesterday I was out with my UVM class, Natural History of Centennial Woods, and we were taking a closer look at poison ivy (Toxicodendron radicans). I'm not a big fan of the "leaves of three let it be" mantra as it prevents people from actually looking at the plant. Besides, strawberries have 3 leaves, as do boxelder, clovers, some Virginia creeper, sarsaparilla, and heaps of other delicious and beautiful plants.
To avoid confusion and cement an understanding of what poison ivy looks like, we created a list of features that would help us distinguish it from other plants. Here are some of the ones I can remember:
- Woody stem
- Three leaves
- Often has toothed edges to leaflets, rarely smooth (or entire)
- Fades to a dull yellow
- Vines have "hairs" on them (see image below)
- Middle leaflet has longer petiole (what attaches leaflet to stem) than two side leaflets
- Middle leaflet symmetrical, lateral ones asymmetrical
- Two leaflets on side look like they're giving the thumbs down
Ecological notes: Also of note on the poison ivy leaves were an abundance of poison ivy leafminers (Cameraria guttifinitella) that appear to be eating the upper layer of cells on the leaves. A couple years ago I watched a catbird eat the berries from poison ivy with great relish. I've seen rabbits nibble leaves, and apparently plenty of other animals will eat the plant and be unaffected by urushiol, the toxic oil in the leaves, stem, and buds that cause us such great irritation. So just because you see an animal eat something doesn't mean you can (particularly don't try and learn which mushrooms to eat by watching red squirrels).
Where: Centennial Woods, and any moderately rich, well-drained but moist soil near you.