Betulaceae Gray

Trees and shrubs , deciduous. Winter buds stipitate or sessile, with either 2--3 valvate scales (stipules) or few to many imbricate scales (or occasionally naked); terminal bud absent. Leaves alternate, spirally arranged, 2--3-ranked, simple; stipules deciduous, distinct; petioles present. Leaf blade sometimes lobed, pinnately veined, margins toothed, serrate to nearly entire; surfaces glabrous to tomentose, abaxially often with resinous glands. Inflorescences unisexual; staminate catkins pendulous, elongate, cylindric, conspicuously bracteate, consisting of crowded, reduced, 1--3-flowered clusters; pistillate inflorescences either of erect to pendulous bracteate catkins, or of compact 2--3-flowered clusters subtended by leafy involucres; bracts often nearly foliaceous or woody in infructescences. Staminate flowers bracteate; stamens (1--)4--6; anthers 2-locular, dehiscing by longitudinal slits, pollen sacs often ± distinct; pistillode sometimes present. Pistillate flowers small, highly reduced; pistil 1, 2(--3)-carpellate; ovary inferior, usually 2-locular proximally, 1-locular distally; placentation axile; ovules 1--2 per locule, pendulous; styles 2, distinct or nearly so; stigmas dry; staminodes usually absent. Fruits nuts, nutlets, or 2-winged samaras, 1-seeded, without multibracteate cupule, often subtended or enclosed by foliaceous hull developed from 2--3 bracts; seed coat membranous; endosperm present, thin at maturity; embryo straight, as long as seed; cotyledons flat or greatly thickened, oily.