Betula L.
Trees or shrubs. Buds sessile, with several imbricate scales. Lvs toothed, few- to many-veined. ♂ catkins formed in autumn, opening in spring often before the lvs; fls with a bract and 2 bracteoles; fls 3 in the axil of each bract; perianth minute, 4-lobed; stamens 2, divided below the anthers. ♀ catkins shorter; fls in groups of 3 each with a bract and 2 bracteoles. Fruiting catkins cylindric to oblong or narrow-ovoid; scales 3-lobed, ± membranous, falling at fr. maturity. Fr. small; wing broad or narrow.
c. 60 spp., N. temperate, especially colder subalpine and subarctic areas. Naturalised sp. 1.
