As a source of walnuts, pecans and hickory nuts and as a source for oil and fine timber. Fossil pollen in the Paleocene and fossil wood from the Eocene.
Flowers are small and greenish, apetalous.
Inflorescence is as a hanging catkin for male flowers, female flowers are erect. Both subtended by bracts. Fruit a drupe or nut. Seed with endosperm lacking. Placentation is basal.