Any of seven species of deciduous, nut-bearing trees of the genus Castanea (order Fagales) native to the Northern Hemisphere and introduced throughout the world. The nuts are actually fruits, with the shells enclosing cotyledons. Trees bear both male and female flowers in late spring but must be cross-pollinated for nut production. Nuts are borne in a spiny involucre or bur that opens to release the nuts in late fall.