Poison oak has leaves that look like oak leaves, usually with three leaflets but sometimes up to seven leaflets per leaf group. It grows as a vine or a shrub. Poison oak is more common in the western United States, but it is also found in the eastern United States and, rarely, in the Midwest. Poison sumac has 7 to 13 leaflets per leaf stem. The leaves have smooth edges and pointed tips. Poison sumac grows as a shrub or small tree.