Flora of North America species comparison

Salix argyrocarpa occurs in Nunavut on the Belcher Islands in Hudson Bay.

In the field, Salix argyrocarpa can be confused with S. glauca. They are not closely related but both have staminate flowers with both abaxial and adaxial nectaries, and tawny floral bracts. In subg. Vetrix, this characteristic occurs also in S. wolfii and sometimes in S. orestera, where it may be attributable to hybridization. See 54. S. wolfii for comment.

Vegetative specimens of Salix argyrocarpa and S. pellita are sometimes difficult to separate. There is no evidence that they hybridize.

Salix argyrocarpa is distinguished from S. pellita by having plants 0.2–1 m, stems delicate, largest medial blades 25–65 mm, 3.3–5.9 times as long as wide, branches highly glossy, not or weakly glaucous, flexible at base, and juvenile blades long-silky; S. pellita has plants 0.5–6 m, stems coarse, largest medial blades 40–123 mm, 4.2–11.3 times as long as wide, branches slightly glossy, often strongly glaucous, highly to ± brittle at base, and juvenile blades glabrous or pubescent, tomentose, or short-silky.

Hybrids:

Salix argyrocarpa forms natural hybrids with S. herbacea, S. pedicellaris, and S. planifolia.

Salix argyrocarpa × S. herbacea has leaf shape and margin dentition of S. herbacea but resembles S. argyrocarpa in having leaves glaucous abaxially, along with some white, silky hairs (especially on proximal leaves), juvenile leaves often revolute or infolded, and ovaries glabrous or with patches of hair, hairs appressed, short, straight or slightly curved, and flattened (having a saberlike appearance). These hybrids are sometimes misidentified as S. arctophila × S. herbacea, but ovary hair type and other characters suggest that S. argyrocarpa is the second parent. Occasional specimens with ferruginous hairs on the leaves suggest the influence of S. pellita or S. planifolia.

Salix argyrocarpa × S. pedicellaris (S. ×dutillyi Lepage) resembles S. pedicellaris in leaf shape and size and in having ovaries usually glabrous, although with patches or streaks of hair, and S. argyrocarpa in having leaves sparsely long-silky abaxially, in margins sparsely crenulate, and in proximal leaves with long-silky hairs abaxially. This hybrid is widespread in northern Quebec (G. W. Argus, unpubl.), where backcrosses seem to occur.

Salix argyrocarpa × S. planifolia (S. ×grayi C. K. Schneider): The collector, C. E. Faxon, noted that it could be distinguished at a distance from S. planifolia by its dull white color and upright branching, and from S. argyrocarpa by being taller. It resembles S. argyrocarpa in having juvenile leaves yellow-green, in catkins shorter and borne on longer flowering branchlets, and in stigmas purplish red. It resembles S. planifolia in having juvenile leaves with ferruginous hairs, and in the general appearance of the catkins (M. S. Bebb 1890).

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

Variety monica applies to the diminutive alpine form that sometimes is recognized in the southern Rocky Mountains (S. J. Brunsfeld and F. D. Johnson 1985); it occurs at higher elevations (2200–4000 m) and is characterized by low growth form (0.14–1 m) and smaller, slightly broader leaves. Although it can be distinctive, it is morphologically confluent with the typical species. B. G. O. Floderus (1939) may be correct in characterizing it as an alpine ecotype.

Salix planifolia and S. pulchra are closely related. Their ranges overlap in northwestern Canada, from northern British Columbia across the southern quarter of the Yukon and northeastward into the Great Bear Lake area. Specimens identified as S. pulchra occur as far northeastward as Coppermine and northeast of Bathurst Inlet; S. planifolia has been recognized in the Mackenzie Delta and Eskimo Lake regions, Northwest Territories. Outlying records should be treated with caution because identification of individual specimens out of context may not be definitive. G. W. Argus (1969, 1973) treated these taxa as subspecies based on their intergradation in northwestern British Columbia, their tetraploid chromosome number, and their similar leaf flavonoid chromatographic patterns, but this taxonomy needs reconsideration.

The primary differences between the two species are stipule size, shape, and persistence and the pubescence on juvenile leaves. Stipules of Salix planifolia are oblong to narrowly elliptic or obovate, 0.8–3 mm (or –4.5 mm at Back River, Northwest Territories), distinctly shorter than petioles, and rarely marcescent for more than one year; stipules of S. pulchra are linear to narrowly oblong, 3–32 mm, usually longer than petioles, and usually marcescent for two or more years. Juvenile leaves of S. planifolia are usually more densely hairy, but vary from glabrescent to sparsely or very densely pubescent or long-silky, whereas juvenile leaves of S. pulchra are usually glabrous or, sometimes, sparsely hairy. The occurrence of rhombic mature leaf blades in S. pulchra sometimes is distinctive, but overlap in leaf shape between the two taxa is very great.

The area of geographic overlap in Yukon and western Northwest Territories is large, but evidence suggests that there the two species may be separated by elevation. In the vicinity of Whitehorse, Yukon, Salix pulchra occurs at higher elevations (1400–1900 m) than S. planifolia (ca. 1000 m); no mixed populations were seen. In Nahanni National Park, Northwest Territories, where S. planifolia is more common than S. pulchra, the latter occurs only in alpine and subalpine habitats (1200–1400 m). Evidence from both localities indicates an elevational separation of the two taxa. Within the area of overlap there is little evidence of intergradation except that S. planifolia has stipules that tend to be more marcescent (40% are marcescent) and sometimes longer (2–3.5 mm) than is usual outside the area of overlap. Nevertheless, specimens from the area of overlap can be easily assigned to one taxon or the other with only a few apparent intermediates. The problem in recognizing intermediacy is that there are only a few, variable characters that separate the two. In contrast, in 1973, G. W. Argus described evidence of hybridization and introgression along the Haines Road in northwestern British Columbia. This was based on variation in stipule size, presence, and persistence in what appeared to be a hybrid swarm. Further data are needed to answer questions about actual hybridization. Are the species separated by habitat or elevation, and are there reproductive barriers? Answers could be gained by population studies and controlled hybridization. Until that is done it is best to treat these taxa as species.

See 76. Salix discolor and 95a. S. alaxensis var. alaxensis for comparative descriptions.

Hybrids:

Salix planifolia forms natural hybrids with S. alaxensis var. alaxensis, S. argyrocarpa, S. brachycarpa var. brachycarpa, S. candida, S. drummondiana, S. humilis, S. pellita, S. pulchra, and S. scouleriana. Hybrids with S. glauca var. cordifolia have been reported (C. K. Schneider 1921) but no convincing specimens have been seen.

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