Salix rotundifolia
Salix ballii
least willow, round-leaf willow
ball's 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 absent or rudimentary on early ones, foliaceous on late ones, apex acute or convex;
petiole shallowly to deeply grooved adaxially, 2.5–7.5 mm, pubescent;
largest medial blade elliptic to obovate, 23–63 × 10–35 mm, 1.4–2.8 times as long as wide, base convex or rounded, sometimes cordate or subcordate, margins flat, serrulate or sinuate, apex convex, rounded, acute, or acuminate, abaxial surface glaucous, glabrous, adaxial slightly glossy, glabrous or sparsely pubescent on midrib, (hairs white, sometimes also ferruginous);
proximal blade margins serrulate or crenulate;
juvenile blade sometimes reddish, glabrous, or midrib sparsely pubescent 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, square, or ovate, 0.3–1 mm;
filaments distinct, glabrous;
anthers yellow, 0.4–0.8 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 square or oblong, 0.2–0.6 mm, shorter than stipe;
stipe 0.8–2 mm;
ovary pyriform, glabrous, beak gradually tapering to or slightly bulged below styles;
ovules 12–18 per ovary;
styles 0.4–1 mm;
stigmas flat, abaxially non-papillate with pointed tip, or broadly cylindrical, 0.2–0.3–0.36 mm.
3.8–8.3 mm.
3–6 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 as leaves emerge; staminate stout, 17–29.5 × 8–11 mm, flowering branchlet 3.5–12 mm; pistillate moderately densely flowered, slender, stout, or subglobose, 10–37.5(–45 in fruit) × 5–12 mm, flowering branchlet 2.5–16 mm;
floral bract brown or bicolor, 0.8–1.6 mm, apex rounded, convex or retuse, abaxially hairy throughout or proximally, hairs straight, curly, or wavy.
Salix rotundifolia
Salix ballii
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.)
Occurrence of Salix ballii in Nunavut is on Charlton Island in James Bay.
Salix ballii differs from S. myrtillifolia in having leaves that are distinctly glaucous abaxially. It was described as S. myrtillifolia var. brachypoda by Fernald, who noted that among the characters that distinguish it from S. myrtillifolia only the presence of leaf glaucescence does not occur elsewhere in S. myrtillifolia. This character may be lost when dried over excessive heat. For example, the only specimen supporting the occurrence of S. myrtillifolia on the Gaspe Peninsula, Quebec, is a badly damaged, poorly dried collection that may have lost its glaucescence in drying. A single character difference such as this usually would not recommend a taxon for species rank, but in this case it may be justified inasmuch as S. ballii and S. myrtillifolia are allopatric. A specimen from Île Couture, Lac Mistassini Region, Quebec, may be an exception but confirmatory collections are needed.
Hybrids:
Salix ballii forms natural hybrids with S. glauca var. cordifolia (S. ×ungavensis Lepage). This sterile hybrid with aborted ovaries is known only from the type locality in northern Quebec. It generally resembles S. glauca var. cordifolia but its ovaries are glabrous except for hairy patches at the base and on the stipe. It is evidently a hybrid involving S. glauca var. cordifolia and a species with glabrous ovaries. E. Lepage (1962) was correct in suggesting that the latter was S. ballii (as S. myrtillifolia var. brachypoda). Both taxa grow together in the area; style and floral bract lengths fall within the range of S. ballii, except for a slight overlap with S. glauca var. cordifolia, and its serrulate to crenulate leaf margins are characteristic of S. ballii.
(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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