Flora of North America species comparison

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.)

Salix arctica is polymorphic and nomenclaturally confusing. E. Hultén (1967, 1971) recognized three subspecies: 1) subsp. arctica (circumpolar from Iceland and the Faeroe Islands across northern Russia, Alaska and Canada to Greenland, south to the Hudson Bay shores of Ontario and the Gaspe Peninsula); 2) subsp. crassijulis (a North Pacific race ranging from Kamchatka and the Russian Far East to the Aleutian Islands, south central and southeastern Alaska along the coast to northern Washington); and 3) subsp. torulosa (ranging from the mountains of central Asia to Kamchatka and the Bering Straits, the Brooks Range and the Rocky Mountains in Alaska, south in the cordillera to southern British Columbia and Alberta). While formal recognition of the three races is appealing, they are actually very difficult or impossible to separate morphologically and have strongly overlapping ranges. Some of the variability may be due to environmental modification (D. B. O. Savile 1964; G. W. Argus 1973; J. H. Soper and J. M. Powell 1985). On Attu Island, Alaska, there are plants to 2 m along with dwarf plants (C. Parker, pers. comm.). Their tall stature cannot be accounted for by habitat alone. The possibility that the complex morphological variability within S. arctica may be ecophenic or ecotypic deserves study.

T. E. Dawson (1987) showed that the pistillate-biased sex ratios in Salix arctica are environmentally controlled; pistillate plants are significantly over-represented in mesic-wet, more fertile sites with low soil temperature, whereas staminate plants are predominant in drier, less fertile sites.

The oldest reported age of Salix arctica is 236 years in East Greenland (H. M. Raup 1965) and 85 years on Ellesmere Island (D. B. O. Savile 1979b).

In northern Greenland, Salix arctica is one of the primary foods for musk ox, arctic hare, and collared lemming (D. R. Klein and C. Bay 1991).

Hybrids:

Salix arctica forms natural hybrids with S. arctophila, S. barclayi, S. fuscescens, S. glauca varieties, S. herbacea, S. ovalifolia, S. pedicellaris, S. phlebophylla, S. polaris, S. rotundifolia, and S. stolonifera.

Salix arctica × S. arctophila (S. ×hudsonensis C. K. Schneider) resembles S. arctophila in its trailing habit and toothed leaf margins, and S. arctica in its hairy leaves and petioles, particularly proximal leaves, and branchlets that are both hairy and glaucous. Ovaries have the flattened, refractive hairs of S. arctica, rather than the ribbonlike hairs of S. arctophila. Some plants have undeveloped ovaries, suggesting infertility. The plants are often sterile. Other putative hybrid specimens resemble S. arctica in having staminate flowers with abaxial and adaxial nectaries and anthers ca. 0.36 mm, and S. arctophila in having glabrous leaves and branchlets. N. Polunin (1940) described intermediates between these species from Burwell, Labrador, and Wakeham Bay, Quebec, but the available specimens were re-identified as either S. arctica or S. arctophila. Polunin (1943) wrote that in Greenland these two species do not “hybridize at all frequently” even where growing “side by side.”

Salix arctica × S. barclayi grows with both parents in tundra above the Tokositna Glacier, Alaska. It resembles S. barclayi in having buds with a distinct and separating inner membrane and stigmas broad and short, and S. arctica in its trailing habit (tundra shrub to 0.23 m) and in stipules absent. It is intermediate in having ovaries hairy only on beaks, and leaves with scattered marginal teeth. It also occurs in southeastern Alaska (G. W. Argus 1973).

Salix arctica × S. fuscescens has the growth form, habitat, and proximal leaves often with ferruginous hairs of S. fuscescens, but ovaries are densely hairy and long-styled as in S. arctica.

Salix arctica × S. glauca varieties: Hybrids are characterized by combinations of characteristics of S. arctica and S. glauca (G. W. Argus 1965, 1973; C. Bay 1992). They resemble S. arctica in its prostrate habit, glaucous branches and buds, sparse branchlet hairiness, dark-colored bracts with long, straight hairs, leaves with long, straight hairs on the abaxial surfaces projecting in a ‘beard’ at the apex, capsules reddish with long stigmas, and dark-colored anthers. They resemble S. glauca in its erect habit, leaves less oblanceolate and without the cuneate base of S. arctica, shorter petioles, bracts light-colored with shorter, wavy hairs, and divided styles. The presence of glaucous branches, as an indication of S. arctica, should be used with caution because S. pellita and S. planifolia also have glaucous branches, but these early flowering species may be phenologically isolated from S. glauca. On Baffin Island, Nunavut, the hybrid may be particularly difficult to recognize because of environmentally induced morphological convergence of S. arctica and S. glauca. On the Belcher Islands, on the east side of Hudson Bay, many plants have brownish to pinkish floral bracts with wavy or straight hairs, glabrate branches, and pilose branchlets, suggesting a hybrid swarm. Within the geographic overlap of S. arctica and S. glauca var. cordifolia, the name S. ×waghornei Rydberg can be applied to this hybrid (Argus 2003). See also A. K. Skvortsov (1971), Argus (1973), and Bay.

Salix arctica × S. herbacea occurring in northern Quebec, the eastern Canadian Arctic Archipelago, and eastern continental Nunavut resembles S. arctica in stems stouter, plants usually not rhizomatous, stipules often present, leaves sparsely glaucous abaxially, sometimes with long straight hairs, catkins more than 20-flowered and arising from lateral buds, and styles to 1.4 mm; and S. herbacea in plants sometimes rhizomatous, leaf margins crenulate, apex sometimes retuse, catkins few-flowered and sometimes arising from subterminal buds, ovaries glabrous, styles sometimes 0.2 mm. These hybrids set some seeds although the parental species have different chromosome numbers (tetraploid or hexaploid versus diploid, respectively). A variant of this hybrid with entire leaf margins was collected in eastern Greenland where both parents grow together. This hybrid resembles S. herbacea in leaf blades 0.5–1.1 times as long as wide with ciliate margins, floral bracts 0.9–1.2 mm, and stigmas 0.3 mm; and S. arctica in leaf margins entire and densely villous ovaries. It is intermediate between the two parents in leaf blades 11.5–14 mm, adaxial surfaces sparsely glaucous, floral bracts sparsely short-hairy, and styles 0.4–0.5 mm.

Salix arctica × S. ovalifolia: An intermediate specimen from Nuvagapak Point, Alaska, it resembles S. arctica in its growth form, leaf shape, and catkin size, and S. ovalifolia in ovaries sparsely hairy and glaucous and stigmas with a flat, non-papillate abaxial surface and pointed tip. It is very different from S. ovalifolia var. glacialis, which E. Hultén (1967) suggested may be the same hybrid.

Salix arctica × S. pedicellaris (S. ×hebecarpa (Fernald) Fernald, based on S. fuscescens var. hebecarpa Fernald), occurs in a raised sphagnum bog on Mt. Albert, Quebec. The population includes typical S. pedicellaris and the hybrids. Hybrids exhibit varying degrees of ovary and stipe hairiness, some juvenile leaf hairiness, and petioles that are deeply grooved and with margins that touch and overlap the groove. All of the specimens clearly indicate that S. pedicellaris is one parent, but the identity of S. arctica as the second parent is not established with certainty.

Salix arctica × S. phlebophylla is an apparently sterile hybrid that resembles S. phlebophylla in its general growth form and small, skeletonized leaves, and S. arctica in leaves thinly glaucous abaxially and ovaries hairy throughout. No seeds were set.

Salix arctica × S. polaris: Dwarf plants, presumed to be this hybrid, are characterized by being rhizomatous, as in S. polaris, but with leaves distinctly glaucous abaxially as in S. arctica. In general, the leaves and catkins are smaller than in typical S. arctica, and sometimes the styles also are shorter, but there is considerable variability. Ovaries are often sparsely hairy throughout, or glabrous at base or throughout except for the beak. The hybrids rarely form seed and may be infertile. Staminate plants may have anthers 0.9–1 mm, as in S. arctica, and leaves not glaucous abaxially, as in S. polaris. There is no single character that defines this hybrid and some plants from mixed populations appear to be intermediate. A specimen from Cornwallis Island, Northwest Territories, which was not rhizomatous but had relatively small, glaucous leaves and catkins with ovaries with patches of hairs especially on beaks, was presumed to be this hybrid, but it could simply be a dwarfed or abnormal specimen of S. arctica. In the Canadian Arctic Archipelago, this hybrid appears on Banks, Cornwallis, and Victoria islands. It is also known from Alaska, British Columbia, Northwest Territories, and Yukon.

Salix arctica × S. rotundifolia resembles S. rotundifolia except for its partially hairy ovaries and leaves glaucous abaxially.

Salix arctica × S. stolonifera occurs in swarms wherever the two parents grow together. The hybrids, and possible intergrades, have ovaries with bare patches or with hairs only on beaks.

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