Betulaceae

Monoecious, mostly deciduous shrubs or trees with perular buds. Pith triangular in section. Innovations often resiniferous. Leaves simple, (in Mal. spp.) spiral, penninerved, crenate or dentate, rarely entire, mostly with domatia in the nerveaxils beneath, in bud mostly folded along the midrib and plicate, often glandularlepidote beneath. Stipules caducous. Catkins unisexual, at least the pendent ♂ ones in terminal panicles above the ♀ ones, the latter mostly in stiff, axillary, poor racemes or terminal on short-shoots.—♂ Flowers in triads, each sustained by a bract. Perianth segments 4 (or less by abortion), mostly connate at the base. Stamens 4, epitepalous; filaments short; anthers glabrous, 2-celled; cells parallel, dehiscing lengthwise. No rudiment of ♀.—♀ Flowers in diads sustained by a bract concrescent with 4 bracteoles, accrescent and woody in fruit, densely packed and imbricate. Perianth 0. Ovary 2-celled, each cell with one anatropous, pendent ovule attached near the apex of the cell; styles 2, free, short, cylindric. Fruiting catkins cone-like. Nut small, compressed, 1-seeded, mostly winged and crowned by the styles. Seed without endosperm; embryo straight; cotyledons flat; testa membranous; embryo straight; endosperm 0; cotyledons flat. Distr. About 20 spp. mainly on the N. hemisphere except in the New World, mostly extra-tropical, in SE. Asia southward to Bengal, N. Assam, Tonkin, and Formosa, in Malaysia only cultivated.