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 numerous minute, down-covered seeds. The leaves turn a lemon yellow in the fall. It is typically found along streams and in swamps. "Salix gooddingii" (Goodding's willow) is sometimes included in "S. nigra" as a variety, as "S. nigra" var. "vallicola" Dudley; when included, this extends the species' range to western North America. However, the two are usually treated as distinct species. Another name occasionally used for black willow is "swamp willow", not to be confused with "Salix myrtilloides" (swamp willow). According to the National Register of Big Trees, the largest black willow tree in the US is in Hennepin, Minnesota.