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 humboldtiana Salix humboldtiana Salix humboldtiana, the Humboldt's willow, is a tree species of willow native to North and South America, growing along watercourses. The species is evergreen or deciduous, depending on climate. It can grow up to 25 meters tall, with a narrow triangular or columnar crown shape. The trunk has a maximum d.b.h. of 80 cm and dark brown to gray fissured bark. Narrow lanceolate leaves up to 15 cm long, with serrate margin and light green color, in temperate climates, it turns yellow in autumn. Catkins 4–10 cm long; male flowers yellowish green, with an ovate-lanceolate bract, six stamens;