Deciduous trees or shrubs, monoecious; buds sometimes enclosed by scales. Leaves alternate, simple, petiolate; margin serrate or crenate, usually with small secondary teeth forming on teeth, or entire; stipules present but shed early. Flowers unisexual, arranged in catkins, produced before new leaves. Male catkins pendulous, elongate, crowded, with 1–3-flowered clusters, bracts usually overlapping; perianth absent or of 1–6 sepals; stamens as many as sepals, filaments connate. Female catkins pendulous or erect, crowded, with 1–3-flowered clusters, bracts overlapping; perianth absent or of 1–6 scales; ovary inferior, carpels mostly 2, each with 2 ovules, but often only one ovule per carpel maturing; styles 1 per carpel, free; staminodes usually absent. Fruit nuts, nutlets, or 2-winged samaras, cupule absent, but nut sometimes subtended or enclosed by 2–3 bracts (not in Victorian species).
6 genera and about 150 species in cool-temperate and boreal areas in the Northern Hemisphere, includes Birch (Betula), Alder (Alnus Mill.), Hornbeam (Ostrya Scop. and Carpinus L.) and Hazelnut (Corylus L.). Only Betula is recorded as naturalised in Victoria.