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 alba Pliny the Elder and others believed willow bark could ease aches and pains and reduce fevers. It has long been used in Europe and China for the attempted treatment of these conditions. This remedy is also mentioned in texts from ancient Egypt, Sumer, and Assyria. The first "clinical trial" was reported by Reverend Edward Stone, a vicar from Chipping Norton in Oxfordshire, England, in 1763 with a successful treatment of malarial fever with the willow bark. The bark is often macerated in ethanol to produce a tincture. The active extract of the bark, called salicin, after the Latin name "Salix",