Betula is a genus of trees (ours). They are known for their tendency to hybridize.
Leaves simple, alternate with straight veins, margins mostly toothed.
Flowers minute, monoecious. Male flowers in drooping, elongate catkins, one scale subtending 3 tiny flowers, pollen wind dispersed; female catkins shorter and stouter, fairly rigid, 3 flowers subtended by a scale, flowers without petals, 2-4 tiny, deciduous, scale-like sepals; blooming in spring.
Fruit is a very small samara, usually a central body with 2 lateral, membranous wings. Wind dispersed from fall into winter.