Salix rotundifolia
Salix caprea
least willow, round-leaf willow
goat willow, hoary willow
erect;
branches yellow-green, yellow-brown, or gray-brown, glabrous;
branchlets yellow-brown or red-brown, glabrous;
branches and branchlets sometimes weakly glaucous.
(marcescent but not skeletonized), stipules usually absent or rudimentary, rarely present on late ones;
petiole (convex, or shallowly to deeply grooved, flat), 0.4–4.6(–5.5) mm, (glabrous adaxially);
largest medial blade (2 pairs of secondary veins arising at or close to base, arcing toward apex) broadly elliptic, subcircular, or circular, 1.9–16.3 × 3–10.5 mm, 0.84–1.17(–2.53) times as long as wide, base rounded or convex, margins flat, entire, ciliate, apex retuse, rounded, convex, or acute, abaxial surface glabrous, adaxial highly glossy, glabrous;
proximal blade margins entire;
juvenile blade glabrous or puberulent.
stipules rudimentary on early ones, foliaceous on late ones, apex acute or convex;
petiole convex to flat adaxially, 7–25 mm, tomentose to glabrescent adaxially;
largest medial blade narrowly elliptic, broadly elliptic, oblanceolate, obovate, or broadly oblong, 50–130 × 25–80 mm, 2–3 times as long as wide, base cuneate or convex, margins slightly revolute, entire, crenate, or sinuate, (glands submarginal or epilaminal), apex acuminate or convex, abaxial surface glaucous, sparsely tomentose or pubescent, hairs erect, wavy, adaxial dull or slightly glossy, sparsely pubescent;
proximal blade margins entire;
juvenile blade green, densely tomentose abaxially, hairs white, sometimes also ferruginous.
abaxial nectary 0.5–1 mm, adaxial nectary narrowly oblong or oblong, 0.8–1.4 mm, nectaries distinct;
filaments distinct or connate less than 1/2 their lengths, glabrous;
anthers ellipsoid or globose, 0.4–0.6 mm.
adaxial nectary oblong or square, 0.4–0.7 mm;
filaments distinct, glabrous;
anthers yellow, ellipsoid or shortly cylindrical, 0.7–1.1 mm.
abaxial nectary present or absent, adaxial nectary usually narrowly oblong or oblong, sometimes flask-shaped, 0.8–2 mm, longer than stipe;
stipe 0.4–0.8 mm;
ovary pyriform, glabrous or puberulent, (hairs in patches, especially on beak), beak slightly bulged below styles;
ovules 7–17 per ovary;
styles connate or slightly distinct distally, 0.5–1 mm;
stigmas flat, abaxially non-papillate with pointed tip, or slenderly or broadly cylindrical, 0.28–0.6 mm.
adaxial nectary oblong, narrowly oblong, or square, 0.4–0.9 mm, shorter than stipe;
stipe 2–2.5 mm;
ovary pyriform, densely short-silky, beak gradually tapering to styles;
ovules 12–14 per ovary;
styles 0.3–0.6 mm;
stigmas slenderly cylindrical, 0.4–0.55–0.6 mm.
3.8–8.3 mm.
6–12 mm.
from subterminal buds; staminate subglobose, stout, or indeterminate, 3.3–18.5 × 2.5–12 mm, flowering branchlet 0.5–9 mm; pistillate moderately densely to loosely flowered (2–15 flowers), stout, subglobose, globose, or indeterminate, 4.5–35 × 2–17 mm, flowering branchlet 0.5–22 mm;
floral bract brown, 1.6–2.8 mm, apex rounded or retuse, entire, abaxially sparsely hairy or ciliate, hairs usually wavy, crinkled or curly, rarely straight.
flowering before leaves emerge; staminate subglobose or globose, 16–39 × 12–30 mm, flowering branchlet 0–3 mm; pistillate densely flowered, stout or subglobose, 27–64 × 10–25 mm, flowering branchlet 0–7 mm;
floral bract dark brown or black, 2–4 mm, apex acute or rounded, abaxially hairy, hairs (white), straight.
= 38.
Salix rotundifolia
Salix caprea
Varieties 2 (2 in the flora).
Salix rotundifolia is closely related to S. polaris, from which it can be separated by its glabrous ovaries and fewer-flowered catkins. They also differ somewhat in leaf venation: S. rotundifolia typically having three main veins arising from the leaf base, often only one or two pair of secondary veins, and no or indistinct tertiary veins; S. polaris typically having pinnate venation, multiple secondary veins, and distinct tertiary veins. Salix rotundifolia consists of two varieties, the diploid var. dodgeana and the hexaploid var. rotundifolia. In general, var. dodgeana is a high alpine species in the southern cordillera of Wyoming and Montana, the St. Elias Mountains in Alaska and Yukon, the Mackenzie Mountains, Northwest Territories, and the Richardson Mountains, Yukon Territory. A diploid specimen of S. rotundifolia in the Cherski Mountains, Yakutia, Russia (B. A. Jurtzev and P. G. Zhukova 1982), which fits var. dodgeana in its 2–3-flowered catkins, relatively small leaves (3.5 × 3.9 mm), and small stomata (490 µm2), may represent an ancestral population. Variety rotundifolia usually occurs at lower elevations in Alaska and in easternmost Chukotka and Wrangel Island, Russia, but elevation separation is not distinct. There is a general correlation between stomatal size and ploidal level (W. Buechler, pers. comm.), but relatively large stomata in some diploid specimens of S. rotundifolia indicates a need for further cytological study. For the present, it is best to recognize the two cytotypes as varieties.
Hybrids:
Salix rotundifolia forms natural hybrids with S. arctica, S. phlebophylla, and S. polaris.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Hybrids:
Salix ×smithiana Willdenow: S. caprea × S. viminalis is an introduced European hybrid commonly naturalized in eastern Canada (New Brunswick, Newfoundland, Nova Scotia, and Prince Edward Island), where it was introduced for coarse basketry. Only pistillate specimens are known and seed-set has not been noted. Its spread is apparently by cultivation and stem fragmentation. It is characterized by: shrubs or trees, 2–10 m; branches yellow-brown, brownish, or gray-brown, pubescent to glabrescent, ± brittle at base, peeled 3–5 year-old branches smooth or striate, striae few, 0–6 mm; branchlets not glaucous, moderately densely pubescent; largest medial leaf blades very narrowly elliptic, narrowly elliptic, or narrowly oblong, 2.8–4.9(–6.4) times as long as wide, margins entire or sinuate, adaxial surfaces pubescent; catkins flowering before leaves emerge; stipes 0.9–2 mm; ovaries pyriform to obclavate, moderately to very densely short-silky; styles 0.5–1.2 mm; stigmas slenderly cylindrical, lobes 0.6–1.2 mm; and capsules 5–7 mm.
Hybrids Salix caprea × S. viminalis and S. cinerea × S. viminalis are commonly recognized in North American floras. They are difficult to separate and their nomenclature is confusing. I am following G. Larsson (1995), who typified S. ×smithiana and cited S. ×sericans (formerly S. cinerea × S. viminalis) and S. caprea × S. viminalis as synonyms. These two S. viminalis hybrids are very similar. Salix caprea × S. viminalis has wood with striae 2–6 mm and leaves usually broadest in the middle; S. cinerea × S. viminalis has decorticated wood with striae 10+ mm and leaves usually broader toward the tip (B. Jonsell and T. Karlsson 2000+, vol. 1). Authentic S. cinerea × S. viminalis has not been seen from the flora area.
See 86. Salix pellita and 98. S. viminalis for more discussion of morphologies.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Pistillate catkins: (3-)4-7-15 flowers; largest medial blades 4.5-8-16.3 mm, 0.92-1.23-2.27 times as long as wide; petioles 0.5-2-4.6 (-5.5) mm; floral bracts: hairs usually wavy, some straight, curly, or crinkled, exceeding bract by 0.32-0.71-1.25(-2.4) mm; pistillate flowers: abaxial nectaries present or absent; 2n = 114. | var. rotundifolia |
1. Pistillate catkins: 2-4-9 flowers; largest medial blades 2.9-6.1-7.4 mm, 0.84-1.5-2.2 times as long as wide; petioles 0.4-1.1-2.8 mm; floral bracts: hairs usually wavy, crinkled, or curly, rarely straight, exceeding bract by 0.1-0.37-0.75 mm; pistillate flowers: abaxial nectaries absent; 2n = 38. | var. dodgeana |
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