Willows, sallows and osiers form the genus Salix, around 400 speciesMabberley, D.J. 1997. The Plant Book. Cambridge University Press: Cambridge. 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 called sallow (the latter name is derived from 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 in height, though spreading widely across the ground. Willows are very cross-fertile and numerous hybrid occur, both naturally and in cultivation. A well known example is the weeping willow (Salix × sepulcralis), very widely planted as an ornamenta