88. Salix planifolia Pursh, Fl. Amer. Sept. 2: 611. 1813.
Salix monica Bebb; S. phylicifolia Linnaeus var. monica (Bebb) Jepson; S. phylicifolia subsp. planifolia (Pursh) Hiitonen; S. planifolia var. monica (Bebb) C. K. Schneider
Shrubs or trees, 0.1-9 m, (sometimes forming clones by layering). Stems (sometimes decumbent); branches yellow-brown, red-brown, or violet, not to strongly glaucous, glabrous or pubescent; branchlets yellow-brown, red-brown, or violet, glabrous, pilose, pubescent, moderately densely villous, or short-silky, (buds caprea-type). Leaves: stipules (sometimes marcescent), rudimentary or foliaceous (small and usually brownish) on early ones, rudimentary or foliaceous on late ones, (narrowly ovate to oblong, 1-2.5(-4.5) mm), apex acute; petiole shallowly grooved adaxially, 2-9(-13) mm, glabrous, pilose, or short-silky adaxially; largest medial blade (sometimes hemiamphistomatous), narrowly oblong, narrowly elliptic, elliptic, or oblanceolate, 20-36-65 × 5-13-23 mm, 1.7-2.8-4.7 times as long as wide, base cuneate or convex, margins sometimes slightly revolute basally, entire, or, sometimes, crenulate or serrulate, apex acute, acuminate, or convex, abaxial surface glaucous, glabrous or sparsely silky, hairs (white, sometimes also ferruginous) straight or wavy, adaxial highly glossy, glabrous or sparsely short-silky; proximal blade margins entire; juvenile blade reddish or yellowish green, glabrous, puberulent, pubescent, or densely long-silky abaxially, hairs white, sometimes also ferruginous. Catkins flowering before leaves emerge; staminate stout, subglobose, or globose, 12-41 × 10-20 mm, flowering branchlet 0-4 mm; pistillate densely flowered, slender, or stout to globose, 15-67 (-70 in fruit) × 8-18 mm, flowering branchlet 0-6 mm; floral bract dark brown or black, 1-3.2 mm, apex acute, convex, or rounded, sometimes 2-fid, abaxially hairy, hairs straight. Staminate flowers: adaxial nectary narrowly oblong or oblong, 0.4-1.1 mm; filaments distinct, glabrous or sparsely hairy basally; anthers purple turning yellow, shortly cylindrical, 0.5-0.7 mm. Pistillate flowers: adaxial nectary oblong, square, or ovate, 0.4-1.3 mm, shorter to longer than stipe; stipe 0.3-0.8 mm; ovary pyriform, short- to long-silky, sometimes slightly bulged below styles; ovules 11-16 per ovary; styles 0.5-2 mm; stigmas slenderly to broadly cylindrical, 0.36-0.52-1.1 mm. Capsules (2.5-)5.5-6 mm. 2n = 76, 57.
Flowering early May-late Jun. Arctic, alpine, subalpine, and boreal meadows and riverbanks, streams, seeps, snowflush areas, treed bogs, fens, sandy-loam, rocky igneous and limestone substrates; 100-4000 m; St. Pierre and Miquelon; Alta., B.C., Man., Nfld. and Labr., N.W.T., Nunavut, Ont., Que., Sask., Yukon; Alaska, Ariz., Calif., Colo., Idaho, Maine, Mich., Minn., Mont., Nev., N.H., N.Mex., Oreg., S.Dak., Utah, Vt., Wash., Wis., Wyo.
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.
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.