Poison sumac (Toxicodendron vernix) is unfamiliar to most hikers because it grows in swamps, marshes, and wet meadows, places that most hikers avoid. In Minnesota, it is found only in nine east-central counties.
Poison sumac looks similar to distant relatives smooth sumac and staghorn sumac, neither of which are poisonous. Poison sumac is distinguished by the untoothed margins of its leaflets. Poison sumac looks nothing like its two closest relatives, eastern and western poison ivy. Eastern poison ivy is a vine with three leaves. Western poison ivy is a small shrub with three leaves. Poison sumac is a tall shrub or very small tree and has compound leaves with 7 to 13 leaflets.
The saps of poison sumac, western poison ivy, and eastern poison ivy all contain the allergenic urushiol. Not all people are allergic to urushiol, but most can become allergic if they are exposed to it. It usually takes 12 to 48 hours for a rash to develop on a previously sensitized person. In some individuals, a single exposure will cause a reaction. In these individuals, the rash will develop in seven to ten days. The lesions last 14 to 20 days. Rashes do not spread and are not contagious. Treatment can dry the blisters, reduce the swelling, and relieve the itching, but it will not speed the healing.