Monoecious trees or shrubs. Leaves alternate, pinnately nerved, deciduous. Flowers small, bracteate; the male in catkins; the female in erect spikes or strobili. Male flowers: Perianth of 2-4 tepals. Stamens 2-4. Female flowers: Perianth absent. Gynoecium bicarpellary, syncarpous; ovary bilocular, each locule with one pendulous ovule; styles 2, free. Fruit a small compressed nut, often surrounded by the fused bract and bracteoles.