Female flowers are produced in short, bright-green, erect catkins. The fruit is a small, winged, nutlet borne on 3-lobed bracts in a pendulous, conelike catkin. Seeds mature in May or June long before other birches, and fall to germinate in the silt from spring flooding. The small leaf scars are crescent-shaped with 3 bundle scars. The chestnut-brown buds are ovoid, and covered with 3 or 4 sometimes hairy scales.
Terminal buds are only present on spur shoots.
Bark on young trees is thin, shiny and cinnamon-brown, peeling into papery, white pieces to reveal the orange inner bark. Older trees have dark, reddish-brown, almost black bark which is deeply furrowed and broken into scaly plates. This birch is the most widely-distributed native birch in the US, occurring on moist sites from Massachusetts to northern Florida, west to Minnesota and Kansas. It is common along the Mississippi and Wapsipinicon rivers in eastern Iowa, and is widely planted throughout the state. Usually found along stream banks and in swampy bottomlands, the river birch grows best in deep, rich, acid, moist soils, but also survives in drier soils.