Willows, sallows, and osiers form the genus Salix, around 400 species of deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions of the Northern Hemisphere. Most species are known as willow, but some narrow-leaved shrub species are called osier, and some broader-leaved species are referred to as sallow (from Old English sealh, related to the Latin word salix, willow). Some willows (particularly arctic and alpine species) are low-growing or creeping shrubs; for example, the dwarf willow (Salix herbacea) rarely exceeds 6 cm (2 in) in height, though it spreads widely across the ground. Willows are very cross-fertile, and numerous hybrids occur, both naturally and in cultivation. A well-known ornamental example is the weeping willow (Salix sepulcralis), which is a hybrid of Peking willow (Salix babylonica) from China and white willow (Salix alba) from Europe.
Contributions by MPF, Curtis Clark, and 18.104.22.168.