Large, pyramidal trees; buds covered by imbricate scales; leaf buds and shoots with cottony tomentose; leaves long-petioled, broadly ovate, deltoid or cordate, sinuately toothed, base 5-nerved; flowers in hairy catkins appearing in advance of leaves, bracts lanceolate, dentate; disc shallow, entire, annular or cupular, usually nectary absent; perianth absent; in male flowers: stamens -2 or more, filaments filiform; female flowers shorter than male; in female flowers: ovary sessile or stipitate, 1-celled, ovules few to many on parietal placenta, styles 2, branched, stigmas 2+2 partite, arms linear; capsule 2-valved, pedicelled.