In the cool temperate regions of the Northern Hemisphere and in the South American Andes. Fossil pollen in the Upper Cretaceaous and some fossil wood from the Eocene.
Flowers are small and as a catkin, the male as a pendulous ament, the female in cymes.
Both are apetalous. Bracts subtend the female flowers. Fruit a nut or winged samara with a large, subtending or enclosing bract. Seed with endosperm lacking. Placentation is axile.