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 nigra as a photodegradation tool. Photodegradation is theorized to work by drawing the target chemical up the roots and stem into the leaves where it is degraded by higher energy radiation provided by the sun. Salix nigra Salix nigra, the black willow, is a species of willow native to eastern North America, from New Brunswick and southern Ontario west to Minnesota, and south to northern Florida and Texas. It is a medium-sized deciduous tree, the largest North American species of willow, growing to tall, exceptionally up to , with a trunk diameter. The bark is dark brown to blackish, becoming fissured