Trees or shrubs, monoecious or dioecious. Stipules 0 (in our species). Leaves alternate, simple, dotted with resinous, aromatic glands. Flowers in dense axillary spikes, forming catkins, unisexual, subtended by a bract. Perianth 0. Male flowers with 2-10(-20) stamens. Female flowers with sessile 1-locular ovary. Stigmas 2, filiform. Fruit an achene or drupe.