Salix humboldtiana |
Salix petrophila |
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Humboldt's willow |
alpine willow, Rocky Mountain willow |
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Habit | Plants 0.02–0.1 m, forming clones by layering. | |
Stems | decumbent or trailing; branches yellow-brown, gray-brown, or red-brown, (often weakly glaucous, dull or slightly glossy), glabrous; branchlets yellow-green or yellow-brown, usually glabrous, sometimes pilose to glabrescent. |
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Leaves | stipules absent or rudimentary; petiole 2–13 mm (longer than subtended bud); largest medial blade usually amphistomatous, very narrowly to broadly elliptic, oblanceolate, or obovate, 19–44 × 7–21 mm, 1.5–4.6 times as long as wide, base cuneate or convex, margins flat, entire, apex acute, acuminate, convex, or rounded, abaxial surface pilose to glabrescent, hairs wavy, adaxial dull or slightly glossy, pilose or sparsely villous to glabrescent; proximal blade margins entire; juvenile blade villous or pilose abaxially, mainly on margin. |
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Staminate flowers | abaxial nectary 0–0.2 mm, adaxial nectary oblong, narrowly oblong, or square, 0.4–1.2 mm, nectaries distinct; filaments distinct or connate less than 1/2 their lengths; anthers ellipsoid, short-cylindric, or globose, 0.4–0.8 mm. |
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Pistillate flowers | adaxial nectary oblong, square, narrowly oblong, or ovate, 0.5–1.2 mm, equal to or longer than stipe; stipe 0.2–0.8 mm; ovary pyriform or obturbinate, sparsely to densely villous, beak gradually tapering to styles; ovules 6–12 per ovary; styles 0.4–1.6 mm; stigmas flat, abaxially non-papillate with rounded or pointed tip, or broadly to slenderly cylindrical, 0.28–0.36–0.6 mm. |
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Capsules | 3.6–5 mm. |
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Salix | humboldtiana Willdenow: Humboldt willow is not known to occur in the flora area. |
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It | is characterized by: trees, 4–25 m; branches highly brittle at base, bud-scale margins distinct and overlapping adaxially; stipules on late leaves rudimentary or foliaceous; largest medial leaf blade usually linear, abaxial surface not glaucous, adaxial dull; pistillate bract deciduous after flowering; stamens 3–7; capsules with distinct, often raised, white veins.; it occurs throughout much of Mexico to central Chile. |
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Catkins | staminate (ca. 50 flowers), 18–32 × 6–13 mm, flowering branchlet 3–13 mm; pistillate moderately densely to loosely flowered, (18–80 flowers), slender or stout, 18–59(–70 in fruit) × 6–15 mm, flowering branchlet 2–40 mm; floral bract tawny or brown, 0.5–3.6 mm, apex acute or rounded, entire or 2-fid, abaxially hairy or ciliate, hairs straight or wavy. |
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2n | = 76. |
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Salix humboldtiana |
Salix petrophila |
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Phenology | Flowering Jul–Aug. | |
Habitat | Alpine snowbeds, meadows, talus slopes and open dry pool beds in spruce-fir forests | |
Elevation | 1700-4000 m (5600-13100 ft) | |
Distribution |
Mexico to central Chile |
CA; CO; ID; MT; NM; NV; OR; UT; WA; WY; AB; BC
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Discussion | Salix humboldtiana is closely related to S. nigra in its generally narrow leaf blades, which are not glaucous abaxially. The two differ in the following characters: S. humboldtiana has leaf blades linear to sometimes narrowly oblong (10–28.6 times as long as wide), ovaries usually ovoid to ellipsoid, ovary walls often stomatiferous and with raised, white veins, and capsule valves relatively thick, slightly recurved. S. nigra has leaf blades usually narrowly lanceolate (6–13 times as long as wide), ovaries pyriform to obclavate, ovary walls neither stomatiferous nor notably veined, and capsule valves relatively thin and strongly recurved. Both species occur in Chihuahua, Mexico. The report by R. I. Lonard et al. (1991) that specimens identified as Salix nigra from the lower Rio Grande, Texas, resemble S. humboldtiana in having strongly veined capsules suggests that S. humboldtiana, or intergrades with that species, may occur in Texas. Attempts to locate a voucher specimen were unsuccessful; because strongly veined capsules are diagnostic, further field study is indicated. An earlier name, Salix chilensis Molina, has been applied to this species; it does not seem to pertain to this taxon (C. K. Schneider 1918). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Salix petrophila is often included in S. arctica (G. W. Argus 1993), but southern cordilleran populations, extending as far north as southern British Columbia and Alberta, seem to be a distinct taxon (Argus 1997). The exact northern limit of this species still needs to be established, but in Alberta it does not seem to extend north of Waterton Lakes National Park, except for a population on springy slopes above Agness Lake, Banff National Park. Suitable alpine habitats between Waterton Lakes and Banff national parks, e.g., Mt. Armstrong, Tornado Mountain, and Crowsnest Pass, should be explored for S. arctica and S. petrophila. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 34. | FNA vol. 7, p. 81. |
Parent taxa | Salicaceae > Salix > subg. Protitea > sect. Humboldtianae | Salicaceae > Salix > subg. Chamaetia > sect. Diplodictyae |
Sibling taxa | ||
Synonyms | S. arctica var. petraea, S. arctica subsp. petraea, S. arctica var. petrophila, S. petrophila var. caespitosa | |
Name authority | Willdenow | Rydberg: Bull. New York Bot. Gard. 1: 268. (1899) |
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