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
Micrurapteryx salicifoliella arbusculoides", "Salix babylonica", "Salix bebbiana", "Salix brachycarpa", "Salix exigua", "Salix glauca", "Salix integra", "Salix interior", "Salix lasiandra", "Salix longifolia", "Salix monticola", "Salix novae-angliae", "Salix planifolia" and "Salix scouleriana"). They mine the leaves of their host plant. The mine is found on the upperside of the leaf, sometimes covering the entire leaf area. It is a flat upperside blotch, initially greenish but later turning brown. The larva chews a hole through the bottom of the mine and exits through it to pupate. The cocoon is often spun on the upperside of a leaf, parallel to its long axis. Micrurapteryx salicifoliella Micrurapteryx