The undersides of its leaves are a much lighter green and are covered with fuzz. Some of these plants may grow clusters of greenish-white berries, but many do not bear fruit. Poison oak grows in the western and southeastern United States, Canada and Mexico. Each leaf has seven to 13 leaflets arranged in pairs. Poison sumac can be distinguished from harmless sumacs by its drooping clusters of green berries.
Harmless sumacs have red, upright berry clusters.
Another simple precaution to protect against exposure to these poisonous plants is to wear long sleeves, long pants, boots and gloves in wooded or grassy areas. But remember, urushiol is an invisible oil that sticks to almost everything. Avoid letting pets run through the woods, as they can carry urushiol easily and can pass it directly to anyone. For more articles on allergies, visit the TheDailyApple's Allergy Center . To discuss poison ivy, poison oak, sumac or other allergy concerns, go to the Allergies Message Board .