Salix babylonica a gold-yellow in autumn. The flowers are arranged in catkins produced early in the spring; it is dioecious, with the male and female catkins on separate trees. "Salix babylonica" was described and named scientifically by Carolus Linnaeus in 1736, who knew the species as the pendulous-branched ("weeping") variant then recently introduced into the Clifford garden in Hartekamp in The Netherlands. Early Chinese cultivar selections include the original weeping willow, "Salix babylonica" 'Pendula', in which the branches and twigs are strongly pendulous, which was presumably spread along ancient trade routes. These distinctive trees were subsequently introduced into England from Aleppo in
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.