Trees or erect shrubs, often dotted with yellow glands and strongly aromatic. Leaves spirally arranged, exstipulate, or stipulate in young plants only, shortly petioled, simple, entire, serrate-dentate or more or less deeply pinnatisect, penninerved. Flowers in axillary, solitary or spiked or racemed catkins, (♂) (♀) or (♂♀); when the inflorescence is (♂♀), then the ♂ flowers below the ♀; each flower subtended by a bract. Sepals and petals absent, or the ♀ with 2 or more minute sepaloid bracteoles. ♂: Stamens 2-20, usually 2-4; filaments free or more or less connate into a column; anthers erect, 2-celled; cells opening by longitudinal slits. Rudimentary ovary, as a rule, absent. ♀: no staminodes. Ovary sessile, 1-celled. Style deeply bifid; branches short or longish, stigmatose on the inner side. Ovule 1, basal, erect, orthotropous. Drupe ovoid, ellipsoid or globose, tuberculate; endocarp hard. Seed erect, not comose; testa membranous; endosperm none; embryo straight; cotyledons plano-convex; radicle short. Distr. Species according to CHEVALIER ca 50, but this number may be greatly reduced. By some authors the genus has been split into 3 genera, but I am inclined to accept only one.