Western American Salix drummondiana and eastern S. pellita have the same close relationship as do S. scouleriana and S. humilis. In Saskatchewan, where their ranges overlap, separation is difficult. The characters shown in the comparison below often overlap but they will usually serve to separate the two. A useful diagnostic vegetative character is the frequent presence in S. pellita of epilaminal glands, which are borne on adaxial leaf surfaces well in from margins.
Salix drummondiana is distinguished from S. pellita by having stipules on early leaves absent or rudimentary, sometimes foliaceous, staminate nectaries 0.3–0.6 mm, largest medial blade margins with submarginal glands, surfaces glabrescent, short-silky, dull or slightly glossy adaxially, petioles villous or velvety adaxially, and juvenile blades short-silky; S. pellita has stipules on early leaves absent or rudimentary, staminate nectaries 0.6–1 mm, largest medial blade margins with epilaminal or submarginal glands, surfaces glabrous, glabrescent, pubescent, or villous, and slightly or highly glossy adaxially, petioles glabrous or pubescent adaxially, and juvenile blades glabrous, glabrescent, pubescent, or tomentose.
Salix drummondiana is distinguished from the similar, but unrelated, S. sitchensis by having branches often strongly glaucous, branchlets sparsely hairy, largest medial blades lorate, narrowly elliptic, elliptic, or oblanceolate, usually narrower, 3–6.2 times as long as wide, margins slightly revolute, and surfaces with white hairs, sometimes also ferruginous; S. sitchensis has branches not glaucous or weakly so, branchlets usually moderately to very densely hairy, largest medial blades elliptic, narrowly oblanceolate, oblanceolate, or obovate, usually slightly broader, 2.1–3.1–4 times as long as wide, margins strongly revolute, and surfaces with white hairs.
Vegetative specimens of Salix drummondiana are distinguished from S. geyeriana by having largest medial blade margins revolute, surfaces usually densely short-silky adaxially, and midribs glabrous; S. geyeriana has largest medial blade margins flat, surfaces usually moderately densely long-silky adaxially, and midribs silky or glabrous.
Salix drummondiana and S. lemmonii can be separated on the basis of variable characters including: branch glaucousness, leaf size, blade hair density and color, catkin size and shape, anther length, petiole length, and chromosome number. Hybridization is rare but may occur in Lassen and Sierra counties, California.
The diploid and tetraploid chromosome numbers for Salix drummondiana have been reported from Wyoming (R. D. Dorn 1975b) and the triploid count from a disjunct population in the Lake Athabasca sand dunes, northern Saskatchewan (Y. Suda and G. W. Argus 1968).
Hybrids:
Salix drummondiana forms natural hybrids with S. alaxensis var. alaxensis, S. irrorata, and S. planifolia.
