Quercus is a genus of trees or shrubs; roots associated with ectomycorrhizal fungi (Smith and Read 1997); stipules deciduous.
Leaves alternate, simple, margins entire to deeply lobed, veins pinnate.
Flowers monoecious, tiny, staminate flowers in catkins, pistillate flowers subtended by a scaly structure that develops into the acorn cap; flowers 1-several at the base of the staminate catkins; flowers blooming before leaves appear.
Fruit a nut partially surrounded by a scaly cap.
Notes .There are two groups of oaks (subgenera), the white oak group (Lepidobalanus) the leaves of these are not bristle-tipped and the acorns mature in one season. The red and black oak groups (Erythrobalanus) have bristle-tipped leaves and the acorns take two seasons to mature. Oaks are notorious for forming hybrids within each group but the subgenera do not cross.