As long as you leave it alone, poison ivy is a pretty cool plant. It takes two forms—as a small shrub or as a creeping vine that can climb tall trees and reach astounding sizes. As almost everyone who grew up in the Midwest knows, its compound "leaves of three" are composed of three leaflets; the central leaflet has a fairly long petiole (leaf stem), while the two bottom leaflets do not. The leaflets are often—but definitely not always—notched once or twice on one side, creating a vaguely mitten-ish outline. The plant can be found just about anywhere, but is particularly common in forest gaps, old fields, riparian locations, and back dunes along the Great Lakes. Seedlings of box elder (Acer negundo) can look very similar to poison ivy in its shrub-like form, but have opposite, rather than alternating, leaves of three.

Most people are allergic to the oils in the poison ivy plant, but other animals appear to be unaffected, and the flowers and berries produced by the plant help sustain a wide variety of birds and insects, while the leaves are sometimes consumed by mammals.

In the upper Midwest—particularly along the Great Lakes—a seond species of poison ivy, Toxicodendron rydbergii (common name: western poison ivy) can be found; it differs by always being shrub-like (never vine-like) and in its bald (rather than fuzzy) leaf-stems.

"leaves of three" feature three leaflets; two are opposite at the base of the petiole, with short stems—while a third, sometimes larger leaflet is in the middle, with a longer stem

in spring, emerging leaves are red and fuzzy

leaflets are not always saw-toothed

older plants climb trees and can become substantial vines

flowers

immature fruits