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.)

Vegetative specimens of Salix hastata often are misidentified as S. barclayi. The characters that indicate S. hastata, or sometimes possible hybrids, are the presence of ferruginous hairs on juvenile leaves or adaxial midribs of mature leaves, leaf margins often entire or with teeth present only distally, and buds with inner membranaceous layer not separating from outer layer.

Salix barclayi is distinguished from S. farriae and S. hastata by having bud-scales with inner membranaceous layer separating from outer layer, juvenile blades glabrous, pilose, or moderately densely villous, largest medial blades oblong, narrowly elliptic, elliptic, oblanceolate, or obovate, margins always toothed, pistillate flowering branchlets 4–24 mm, staminate flowering branchlets 0–17 mm, floral bracts brown to black, moderately densely hairy, anthers 0.6–1 mm, styles 0.6–2.5 mm, and stipes 0.4–1.5 mm; S. farriae has bud-scales with inner membranaceous layer separating from outer layer, juvenile blades glabrous or sparsely villous, largest medial blades narrowly elliptic to elliptic, margins usually entire, pistillate flowering branchlets 1.5–14 mm, staminate flowering branchlets 1–5 mm, floral bracts bicolor, brown, or black, sparsely hairy, anthers 0.3–0.6 mm, styles 0.3–1.2 mm, and stipes 0.5–1.2 mm; and S. hastata has bud-scales with inner membranaceous layer not separating from outer layer, juvenile blades sparsely pubescent, largest medial blades narrowly to broadly elliptic, narrowly ovate, or ovate, margins usually entire, pistillate flowering branchlets 1.5–9 mm, staminate flowering branchlets 1–7 mm, floral bracts brown or bicolor, sparsely hairy, anthers 0.4–0.6 mm, styles 0.2–0.48 mm, and stipes 0.4–1.2 mm.

Hybrids:

Salix barclayi is morphologically highly variable. While it is possible that much of this variability is inherent, hybridization and introgression have played an important role.

Salix barclayi forms natural hybrids with S. arctica, S. barrattiana, S. brachycarpa, S. cascadensis, S. commutata, S. farriae, S. hastata, S. hookeriana, S. richardsonii, and S. stolonifera.

Salix barclayi × S. barrattiana is characterized by oily buds that stain the pressing paper yellow, and leaves often entire, or nearly so, and closely gland-dotted, and not glaucous abaxially. Some hybrids resemble S. barclayi in having ovaries glabrous and leaves serrulate and slightly glaucous abaxially, while others resemble S. barrattiana in having stipules marcescent and leaves short-hairy on both surfaces and not glaucous abaxially, but it is the presence of the oily buds characteristic of S. barrattiana that indicates their hybridity. The hybrids usually were from populations that included both parents. An important ramification of the discovery of this hybrid is that the specimen on which the chromosome number for S. barclayi (R. D. Dorn 1976) is based is a plant with oily buds, which has leaves with a mixture of weakly developed teeth and closely gland-dotted, entire margins, and is putatively identified as this hybrid. Further chromosome counts for S. barclayi are needed. Hybrids are known in British Columbia from the mountains in the Peace and Liard river basins, and in Mt. Robson National Park. The hybrid should be suspected wherever the parents occur together.

Salix barclayi × S. cascadensis, collected in Washington in alpine mats growing with both parents, has ovaries with hairy beaks indicating hybridization.

Salix barclayi × S. commutata resembles S. barclayi in having leaves glaucous abaxially, and S. commutata in having leaves hairy on both surfaces (northern British Columbia, Unalaska Island, and southeastern Alaska).

Salix barclayi × S. farriae is represented by a series of specimens resembling S. barclayi but with ferruginous hairs on juvenile leaves or on adaxial midribs of mature leaves, found from the Rocky Mountains of Alberta to southern Yukon and adjacent Northwest Territories. Similar specimens from Alaska may be the hybrid S. barclayi × S. hastata. Both of these hybrids require further study. See 63. S. hastata and 64. S. farriae.

Salix barclayi × S. hookeriana hybrids or introgressants at Tanis Lake, Alaska, have subentire leaves and stipes glabrous or hairy.

Salix barclayi × S. richardsonii hybrids and intergrades are relatively common in Alaska, British Columbia, and Yukon. They resemble S. barclayi in having catkins borne on distinct flowering branchlets, small stipules, anthers yellow and longer, and S. richardsonii in having marcescent stipules, branchlets and branches coarsely villous with spreading hairs, pistillate nectaries longer than stipes, and catkins sometimes on relatively short flowering branchlets.

Salix barclayi × S. scouleriana has the general appearance of S. barclayi but the densely hairy ovaries and the relatively long stigmas (0.9–0.92 mm) of S. scouleriana. It was growing with S. barclayi in openings created in white spruce by bark beetles.

Salix barclayi × S. stolonifera is characterized by relatively small leaves with irregularly serrulate margins, some young leaves reddish green, and a prostrate habit (G. W. Argus 1973).

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