There are two main types of Poison Oak - Western(Pacific) & Atlantic.
Western Poison Oak is only found on the Pacific Coast of the US and Canada. It can grow as a dense shrub or a climbing vine. Like Poison Ivy, leaves are a compound of three leaflets; however, the leaflets tend to have scalloped edges and often resemble the leaves of an oak tree. The color of the leaves range from light green to yellow-green to bright red, depending on the seasons. White flowers will also form in the spring and turn into white or tan berries as they develop. It is common that in the winter, Poison Oak plants will loose their leaves and only berries will remain. It is important to understand that even without the leaves, the Urushiol oil is present.
Atlantic Poison Oak is found growing in forests, thickets and dry,sandy fields, usually throughout the Southeastern United States westward to Texas and Oklahoma. It can grow as an erect shrub up to 3 foot tall. The leaves are also a compound of three leaflets, which are usually hairy and often resemble white oak leaves. The color of the leaves range from green to yellow or orange in the fall. The berries are usually yellowish or greenish.