Family composed of 6 genera and about 235 species of deciduous trees and shrubs, distributed in temperate and cold regions of the Northern Hemisphere and the Andes. In North Africa 2 genera are represented.
Key to genera
1 Leaves triangular. Infructescence longly cylindrical, not lignified, dehiscent Betula
1 Leaves suborbicular. Infructescence ellipsoid, woody, not dehiscent Alnus
Updated by: G. Benítez, J. Molero Mesa & J. Charco.