Trees or shrubs. Leaves alternate, distichous, simple, entire to serrate, often inequilateral at the base. Stipules small, deciduous, free or united. Inflorescence consisting of small cymes or racemes or the female flowers solitary in the leaf-axils. Flowers small, hermaphrodite, unisexual or polygamous, often zygomorphic. Tepals 3—8, free or more or less connate, imbricate or valvate. Stamens as many as the tepals, epitepalous; filaments distinct, not incurved in the bud; anthers 2-celled with longitudinal dehiscence. Ovary superior, usually 1-locular; styles 1 or 2, linear, stigmatic along the inner surface of the upper part. Ovule solitary, pendulous from the top of the cell, anatropous or amphitropous. Fruit a samara, nut or drupe. Embryo straight or curved. Endosperm scanty or wanting. Cotyledons usually flat. About 150 species in 15 genera in tropical and temperate regions, especially in the northern hemisphere.