The adage “Leaves of Three, Let It Be” is actually a good suggestion. Poison oak and ivy are master imitators, taking on the leaf shape of the plants around them and making them difficult to identify. The three-leaf pattern gives them away, so you’re safer staying away from any three-leafed plant unless you’re sure it isn’t poisonous.
Poison oak and poison ivy can be difficult to tell apart, and the leaf shape varies from region to region.
The leaves may be serrated, round, or oak-like depending on what other foliage is around the poison oak plants. They may be shiny, or not. They may have a red tinge, or not. The plant itself may be single stalks of three leaves close to the ground. Or a bush. Or a vine climbing up a tree.
A large poison ivy vine growing up a tree.