Willow are very cross-compatible, 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. The hybrid cultivar 'Boydii' has gained the Royal Horticultural Society's Award of Garden Merit. Numerous cultivars of "Salix" L. have been developed and named over the centuries. New selections of cultivars with superior technical and ornamental characteristics have been chosen deliberately and applied to various purposes. Most recently, "Salix" has become an important source for bioenergy production and for
Salix babylonica to northern China, "Salix matsudana" (Chinese willow), is now included in "Salix babylonica" as a synonym by many botanists, including the Russian willow expert Alexey Skvortsov. The only reported difference between the two species is "S. matsudana" has two nectaries in each female flower, whereas "S. babylonica" has only one; however, this character is variable in many willows (for example, crack willow "[Salix fragilis]" can have either one or two), so even this difference may not be taxonomically significant. "S. babylonica," especially its pendulous-branched ("weeping") form, has been introduced into many other areas, including Europe and the southeastern United States,