A genus (Quercus) of trees, some of which are shrubby, with about 200 species, mainly in the Northern Hemisphere. About 50 species are native in the United States. All oaks have scaly winter buds, usually clustered at the ends of the twigs, and single at the nodes. The fruit is a nut (acorn) surrounded at the base by an involucre, the acorn cup. The pith is star-shaped. The leaves are simple and usually lobed.