The family Fagaceae , also called beech family , is a family of flowering plants . It comprises about 900 species of both evergreen and deciduous trees and shrubs , which are characterized by alternate simple leaves with pinnate venation , unisexual flowers in the form of catkins , and fruit in the form of nuts . The family Fagaceae , or beech family , comprises about 900 species of both evergreen and deciduous trees and shrubs , which are characterized by alternate simple leaves with pinnate venation , unisexual flowers in the form of catkins , and fruit in the form of cup-like ( cupule ) nuts .