Willow, a group of shrubs and trees that grow chiefly in temperate areas of the Northern Hemisphere. A few kinds of willows grow in the tropics, and some grow in the Arctic. There are about 170 species of willows, 65 of which grow in North America.

Most willows grow chiefly on or near riverbanks and lakeshores. Willow leaves are typically slender and pointed, although they are broad in the peach-leaved willow and some other species. The female flowers grow in catkins (clusters around a central axis), usually on separate trees from the male flowers. Sometimes male and female flowers grow on the same tree, and even on the same catkin. Willow seeds bear tufts of down by which they are carried away by the wind. The seeds die unless they fall in damp places within a few hours. Willows can be easily grown from cuttings set in moist sand. Willow twigs readily take root when they fall in mud.

Willows are planted as ornamentals and shade trees, and to prevent river banks from eroding. Willow shoots, called osiers, are used to make baskets and wicker furniture. Willow bark is used in tanning. The bark and leaves contain salicin, a pain-killing drug. Willow wood is used to make a number of products, including artificial limbs, cricket bats, furniture, coffins, barrels, boxes, crates, paper pulp, and charcoal for black powder.

The black willow, which grows to more than 100 feet (30 m) tall, is the willow most used for lumber in the United States. It is native to eastern North America and grows best in the lower Mississippi Valley. The white willow grows to more than 80 feet (24 m) tall. It was introduced into North America from Europe. The crack willow is named for its brittle twigs, which break off in strong winds. It has become naturalized in North America from Europe and Asia.

The pussy willow of eastern North America is valued for its decorative, gray, silky catkins. The weeping willow has graceful, drooping branches. It was introduced into North America from its native China. The weeping willow is widely grown as an ornamental.

Willows form the genus Salix of the willow family, Salicaceae. The black willow is S. nigra; white, S. alba; crack, S. fragilis; pussy, S. discolor; weeping, S. babylonica.