Any of about 450 species of ornamental and timber trees and shrubs that make up the genus Quercus in the beech family, found throughout temperate climates. Oaks are deciduous trees that bear spring catkins (male flowers) and spikes (female flowers) on the same tree. The leaves have lobed, toothed, or smooth margins. The fruit is the acorn. They are hardy and long-lived shade trees. White oaks have smooth leaves and rapidly germinating sweet acorns; red, or black, oaks have bristle-tipped leaves and bitter, hairy acorns. Red- and white-oak lumber is used in construction, flooring, furniture, millwork, barrel making, and the production of crossties, structural timbers, and mine props. The genus includes many ornamentals and natural hybrids.