A family of deciduous shrubs and trees in which the leaves are simple, with stipules. The flowers are unisexual, the males borne in catkins with 2–12 stamens; the females clustered, the ovary inferior and composed of two fused carpels. They are wind-pollinated in early spring. The fruit is a one-seeded nut, often winged. The family includes the birches (Betula), alders (Alnus), hornbeams (Carpinus), and hazels (Corylus). There are 6 genera and about 150 species occurring in the northern hemisphere, extending to the tropical mountains.
Subjects: Plant Sciences and Forestry.