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A shrub or low tree not more than 25 ft high; young shoots purplish brown, at first downy. Leaves oblong, oval, or obovate, tapered at both ends, toothed except towards the base, 2 to 5 in. long, 5⁄8 to 11⁄4 in. wide, at first somewhat downy, soon becoming glabrous, bright green above, and blue-white beneath; stalk 1⁄4 to 1 in. long. Catkins opening in March and April on the leafless shoots; males up to 11⁄2 in. long, cylindrical; stamens two, with glabrous stalks; female catkins up to 3 in. long in fruit. Ovary beaked, downy, with a distinct style.
Native of the eastern United States and Canada; introduced in 1811. It is rather striking in its deep brown branchlets and very glaucous under-surface of the leaves. This character serves to separate it from S. caprea and S. cinerea, and there is the further difference that in those species the stigma is almost sessile.
It is, however, allied to the Old World sallows. So too are:
S. humilis Marsh. – A shrub to 10 ft high with downy or glabrous branchlets. Leaves up to 4 in. long, narrowly to broadly oblanceolate, dull green above, underside clad with persistent short, curled hairs or becoming almost glabrous, margins entire or slightly wavy-toothed. Stipules narrow or wanting. Catkins sessile, before the leaves, 1⁄2 to 1 in. long; scales blackish, hairy. Anthers reddish or purplish. Ovary with a long beak, downy, stalked; stigmas almost sessile. A variable species, widely distributed in eastern and central N. America. Introduced to Kew from the Arnold Arboretum in 1889 and again in 1908 (a different form).
S. tristis Ait. S. humilis var. microphylla (Anderss.) Fern. – Very near to S. humilis and from the same region, but dwarfer (to 3 or 4 ft) and smaller in all its parts. Leaves narrowly oblanceolate, up to 2 in. long and 1⁄2 in. wide. Introduced 1765.
[S. tristis Ait.] – Dr George Argus has pointed out that the correct name for this species is S. occidentalis Walt., wrongly considered by Schneider and other authorities to be a synonym of S. humilis (Brittonia, Vol. 36, pp. 328-9 (1984)).