Spring and summer in Alabama bring a glorious burst of greenery, including the hiker’s scourge: poison ivy and poison oak. Here’s a refresher from the experts at the Alabama Cooperative Extension System on how to identify them – and their very different-looking cousin, poison sumac – before any unfortunate encounter.

Leaves of three, let it be

The leaves of poison ivy and poison oak have three leaflets. The leaflets are commonly 2 to 8 inches long and 3⁄4 to 5 inches wide, and they have scattered, jagged teeth along the edges. Some have a larger tooth or lobe close to the bottom edge, giving them a mitten-like shape.

The teeth on the leaflets of poison oak tend to be more rounded, while those of poison ivy are more pointed. There is often a reddish spot where the two bottom leaflets join together.

Poison ivy grows as a vine that may run along the ground or up the sides of trees, houses, or other vertical surfaces. The vines can reach more than 2 inches in diameter. Larger vines often appear “hairy” due to tiny roots that extend from the vine. In contrast, poison oak is more shrub-like, and its leaves often are crowded near the tips of upright stems, which can reach 3 feet tall. Both species produce clusters of small white to tan fruit.

Poison ivy is found in a wide variety of habitats but is especially common in wooded areas, along forest edges, and in urban green spaces. Poison oak is typically found in dry pine and scrub oak forests or other dry sites.

Poison ivy (Alabama Cooperative Extension System)

Poison oak (Alabama Cooperative Extension System)

Poison sumac

Poison sumac (Alabama Cooperative Extension System)

Poison sumac is a close relative of poison ivy and poison oak, but it looks very different.

Poison sumac leaves have seven to fifteen leaflets that are commonly 2 to 4 inches long and 3⁄4 to 2 inches wide. The leaflets, which are arranged along the stem in pairs, are oblong with sharply pointed tips and smooth or somewhat wavy edges. The stems and leaf stalks often are a bright red color.

Poison sumac grows as a shrub or small tree, reaching up to 20 feet tall, and is typically found only in open or wooded swampy areas. Smooth, greenish white fruit produced during late summer may persist on the plant through the fall and winter.

Safe look-alikes

Virginia Creeper (Alabama Cooperative Extension System)

Virginia creeper (Parthenocissus quinquefolia) and poison ivy often grow together and are frequently confused with each other.

Young Virginia creeper leaves or those that have been damaged may occasionally have three leaflets, but most have five. Poison ivy never has five leaflets. Plants of both species often have a reddish center where the leaflets join.

Another difference is Virginia creeper vines are much less hairy than poison ivy vines. Virginia creeper has fewer, more widely spaced rootlets, and some rootlets have small attachment disks at the ends. Only rarely does contact with Virginia creeper leaves or stems cause an allergic reaction in sensitive individuals. The plant is generally considered harmless, but the fruit can be harmful if eaten.

Box elder (Acer negundo) seedlings have leaves with three leaflets and can look like poison ivy at first glance.

Box elder leaves, however, are arranged opposite each other along the stem; poison ivy leaves are arranged alternately along the stem.

Box elder (Alabama Cooperative Extension System)

Climbing hydrangea (Decumaria barbara) vines are hairy and may appear very similar to poison ivy, but they have opposite, simple leaves with smooth edges or just a few shallow teeth.

Fragrant sumac (Rhus aromatica) is often mistaken for poison oak, and both grow in similar habitats. One difference is that the leaflets of fragrant sumac are attached at a single point, while the terminal leaflet of poison oak has a short stem. Also, the fruit of the fragrant sumac plant is red.

Smooth sumac (Rhus glabra) and winged sumac (Rhus copallinum) are commonly occurring shrubs that may be mistaken for poison sumac, but there are several clear differences. The leaflets of smooth sumac have teeth along the edges and are greater in number (eleven to thirty-one) than those seen in poison sumac Winged sumac is easily identified by the leafy wings along the leaf stalk. Neither species is likely to cause skin irritation, although some people may be sensitive to the sap. The fruits of both nonpoisonous sumacs are red, unlike those of poison sumac.

Of course, a good rule of thumb to follow for any look-alike plant is: If you’re not sure, don’t touch it!

A version of this story originally appeared on the Alabama Cooperative Extension System website.