Any of about 40 species of short-lived ornamental and timber trees and shrubs of the genus Betula , the largest genus of the family Betulaceae, which also contains alder s, filbert s, Carpinus (hornbeam), and the genera Ostrya and Ostryopsis .
Birches are found throughout cool regions of the Northern Hemisphere; other members of the family Betulaceae are found in temperate and subarctic areas of the Northern Hemisphere, in tropical mountains, and in South America through the Andes as far south as Argentina. Leaves are simple, serrate, and alternate; male and female flowers ( catkin s) are borne on the same plant. The fruit is a small nut or short-winged samara (dry, winged fruit). Birches produce economically important timber. Oil obtained from birch twigs smells and tastes like wintergreen and is used in tanning Russian leather (see tanning ).