Flora of North America species comparison

Salix hookeriana is primarily a coastal species occurring from northern California northward to Oregon, Washington, and southern Vancouver Island, with disjunct populations on Queen Charlotte Islands, British Columbia, and northward to Yakatut Bay, Turnagain Arm, and Kodiak, Alaska. It was treated by G. W. Argus (1973) and R. D. Dorn (2000) in a broad sense because of an absence of strong distinguishing characters and intergradation in characters that could be used to divide it. It is highly variable and three very similar taxa have been named: S. amplifolia, S. hookeriana (including vars. tomentosa and laurifolia), and S. piperi. Although extremes of these taxa sometimes are recognizable, the intergradation displayed is so great that even attempts to recognize them as varieties are thwarted. The amplifolia variant in Alaska is characterized by having only white leaf hairs, hairy ovaries, no stipules, and catkins often borne on distinct flowering branchlets, but variation can occur within the same population, and typical S. hookeriana on Vancouver Island sometimes displays the same characteristics. The piperi variant, an inland population in western Oregon and Washington, is usually recognized by local botanists as different from coastal populations. It is characterized by leaves and branchlets soon becoming glabrate and stipules prominent. These characteristics, however, sometimes appear in northern California coastal populations, and some inland populations in Oregon include very hairy individuals that are indistinguishable from coastal variants of S. hookeriana. In general, very hairy populations of S. hookeriana are probably an adaptation to marine coastal environments, but some variation may be due to hybridization and introgression with S. scouleriana. Inland populations suggest the influence of S. lasiolepis. Two hexaploid chromosome numbers reported for S. hookeriana from Vancouver Island (R. L. Taylor and S. Taylor 1977) and Queen Charlotte Islands (R. L. Taylor and G. A. Mulligan 1968), British Columbia, indicate that hybridization has played a role in the evolution of this complex. It is possible that each variant of S. hookeriana has had a different, possibly even recurrent, polyploid origin. Further cytological and genetic study is indicated.

The following comparisons may help to distinguish Salix hookeriana, S. lasiolepis, and S. scouleriana.

Vegetative specimens of Salix hookeriana can be distinguished from S. lasiolepis by having floral buds ellipsoid, beaks distinctly long-tapered, densely long-hairy (villous), red-brown, blades usually pilose, villous, or woolly on abaxial surfaces, usually 18–63 mm wide, and 1.5–4.2 times as long as wide; S. lasiolepis has floral buds ovoid, beaks inconspicuous and blunt, sparsely to moderately densely short-hairy (velvety), yellowish to red-brown, blades usually tomentose on abaxial surfaces, usually 6–32 mm wide, and 3.2–9.6 times as long as wide.

Salix hookeriana is distinguished from S. scouleriana by having branchlets with spreading hairs (woolly or tomentose to glabrate), petioles usually pilose to tomentose, blades typically narrowly elliptic but variable, stigmas 0.3–0.74, short in relation to styles (0.6–2.3 mm), and pistillate nectaries 0.5–1.4 mm, shorter or longer than stipes; S. scouleriana has branchlets usually with short, erect hairs (velutinous), sometimes spreading (villous or tomentose), petioles velvety or villous adaxially, blades typically oblanceolate but variable, stigmas 0.4–1.04 mm, long in relation to styles (0.2–0.6 mm), and pistillate nectaries 0.2–0.8 mm, shorter than stipes.

Hybrids:

Salix hookeriana forms natural hybrids with S. barclayi and S. scouleriana. Variation in some S. hookeriana populations suggests hybridization with S. lasiolepis but no positive identifications have been made. R. D. Dorn (2000) doubted that hybridization in California between these species with different chromosome numbers was possible, but species with different chromosome numbers do hybridize [for example, S. athabascensis (4x) × S. pedicellaris (2x)]; synthetic hybridization studies are indicated.

Salix hookeriana × S. scouleriana: Plants from southern British Columbia with leaves similar to S. hookeriana but with prominent stipules, catkins both erect and recurving, and relatively long stigmas were thought by J. K. Henry (1915) to be this hybrid.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

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.

(Discussion copyrighted by Flora of North America; reprinted with permission.)