a natural family of chiefly monoecious trees and shrubs, including beeches, chestnuts, and oaks; it includes the genera Castanea; Castanopsis; Chrysolepis; Fagus; Lithocarpus; Nothofagus; and Quercus.

The family Fagaceae, or beech family, is characterized by alternate leaves with pinnate venation, flowers in the form of catkins, and fruit in the form of nuts, one to seven in a scale or spiny husk that may or may not enclose the nut. The best-known group of this family is the oaks, genus Quercus, the fruit of which is called an acorn. The husk of the acorn in most oaks only forms a cup in which the nut sits.