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least willow, round-leaf willow

meadow willow, skeleton-leaf willow, slender willow

Habit Plants 0.005–0.05 m, (dwarf), forming clones by rhizomes. Plants 1–6 m. Stems: branches red-brown or violet, not or weakly glaucous, (dull or slightly glossy), puberulent; branchlets yellow-green to red-brown, sparsely pubescent or moderately densely velvety, (buds alba-type or intermediate).
Stems

erect;

branches yellow-green, yellow-brown, or gray-brown, glabrous;

branchlets yellow-brown or red-brown, glabrous;

branches and branchlets sometimes weakly glaucous.

Leaves

(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 or absent;

petiole shallowly grooved adaxially, 3–11 mm, pubescent, or velvety to glabrescent adaxially;

largest medial blade lorate or very narrowly elliptic, 38–110 × 6–19 mm, 5–9 times as long as wide, base cuneate or convex, margins flat to slightly revolute, entire, serrate, serrulate, or spinulose-serrate, apex acute to acuminate, abaxial surface glaucous, densely long-silky to glabrescent, hairs (white, sometimes also ferruginous), adaxial dull or slightly glossy, glabrous or sparsely pubescent, (hairs white, sometimes also ferruginous);

proximal blade margins sometimes serrulate;

juvenile blade moderately densely long-silky abaxially, hairs white, sometimes also ferruginous.

Staminate flowers

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 square, ovate, or oblong, 0.3–0.7 mm;

filaments distinct, hairy basally;

anthers purple turning yellow, ellipsoid or globose, 0.4–0.6 mm.

Pistillate flowers

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 to ovate, 0.3–0.9 mm;

stipe 1.5–4 mm;

ovary pyriform, beak abruptly tapering to styles;

ovules 6–12 per ovary;

styles 0–0.5 mm;

stigmas slenderly to broadly cylindrical, 0.26–0.4–0.8 mm.

Capsules

3.8–8.3 mm.

5–9 mm.

Catkins

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 to globose, 12–29 × 6–17 mm, flowering branchlet 0.8–3 mm; pistillate loosely flowered, stout to globose, 12–39 × 6–18 mm, flowering branchlet 1–11 mm;

floral bract brown, tawny, light rose, or bicolor, 1–2 mm, apex rounded, abaxially sparsely hairy, hairs straight.

2n

= 38.

Salix rotundifolia

Salix petiolaris

Phenology Flowering mid Apr-mid Jun.
Habitat Sedge meadows, openings in moist, low, rich deciduous woods, sandy or peaty wet prairies, lakeshores
Elevation 10-2700 m (0-8900 ft)
Distribution
from FNA
AK; MT; WY; NT; YT; e Asia
[WildflowerSearch map]
[BONAP county map]
from FNA
CO; CT; IA; IL; IN; MA; ME; MI; MN; ND; NE; NH; NJ; NY; OH; PA; SD; VT; WI; AB; BC; MB; NB; NS; NT; ON; PE; QC; SK
[WildflowerSearch map]
[BONAP county map]
Discussion

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.)

See 107. Salix sericea for a comparative description.

Because reproductive barriers between Salix petiolaris and S. eriocephala are weak, A. Mosseler (1990) suggested that their morphological variability may be due to interspecific gene flow.

Hybrids:

Salix petiolaris forms natural hybrids with S. bebbiana, S. candida, S. eriocephala, S. famelica, S. pellita, and S. sericea. Hybrids with S. alba have been reported (M. L. Fernald 1950) but no convincing specimens have been seen. Controlled pollinations with S. discolor produced no seed (A. Mosseler 1990).

Reports of Salix petiolaris × S. sericea from Massachusetts and Pennsylvania (C. K. Schneider 1921) probably refer to the densely sericeous variant of S. petiolaris. It is sometimes named S. ×subsericea (Andersson) C. K. Schneider but does not seem to be a hybrid (G. W. Argus 1965, 1986; E. G. Voss 1972–1996, vol. 2).

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

Key
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
Source FNA vol. 7, p. 69. FNA vol. 7, p. 152.
Parent taxa Salicaceae > Salix > subg. Chamaetia > sect. Herbella Salicaceae > Salix > subg. Vetrix > sect. Geyerianae
Sibling taxa
S. alaxensis, S. alba, S. amygdaloides, S. arbusculoides, S. arctica, S. arctophila, S. argyrocarpa, S. arizonica, S. athabascensis, S. atrocinerea, S. aurita, S. babylonica, S. ballii, S. barclayi, S. barrattiana, S. bebbiana, S. bonplandiana, S. boothii, S. brachycarpa, S. breweri, S. calcicola, S. candida, S. caprea, S. caroliniana, S. cascadensis, S. chamissonis, S. chlorolepis, S. cinerea, S. columbiana, S. commutata, S. cordata, S. daphnoides, S. delnortensis, S. discolor, S. drummondiana, S. eastwoodiae, S. elaeagnos, S. eriocephala, S. euxina, S. exigua, S. famelica, S. farriae, S. floridana, S. fuscescens, S. geyeriana, S. glauca, S. gooddingii, S. hastata, S. herbacea, S. hookeriana, S. humboldtiana, S. humilis, S. interior, S. irrorata, S. jejuna, S. jepsonii, S. laevigata, S. lasiandra, S. lasiolepis, S. lemmonii, S. ligulifolia, S. lucida, S. lutea, S. maccalliana, S. melanopsis, S. monochroma, S. monticola, S. myricoides, S. myrsinifolia, S. myrtillifolia, S. nigra, S. niphoclada, S. nivalis, S. nummularia, S. orestera, S. ovalifolia, S. pedicellaris, S. pellita, S. pentandra, S. petiolaris, S. petrophila, S. phlebophylla, S. planifolia, S. polaris, S. prolixa, S. pseudomonticola, S. pseudomyrsinites, S. pulchra, S. purpurea, S. pyrifolia, S. raupii, S. reticulata, S. richardsonii, S. scouleriana, S. sericea, S. serissima, S. sessilifolia, S. setchelliana, S. silicicola, S. sitchensis, S. sphenophylla, S. stolonifera, S. taxifolia, S. thurberi, S. tracyi, S. triandra, S. turnorii, S. tweedyi, S. tyrrellii, S. uva-ursi, S. vestita, S. viminalis, S. wolfii, S. ×fragilis, S. ×jesupii, S. ×pendulina, S. ×sepulcralis, S. ×smithiana
S. alaxensis, S. alba, S. amygdaloides, S. arbusculoides, S. arctica, S. arctophila, S. argyrocarpa, S. arizonica, S. athabascensis, S. atrocinerea, S. aurita, S. babylonica, S. ballii, S. barclayi, S. barrattiana, S. bebbiana, S. bonplandiana, S. boothii, S. brachycarpa, S. breweri, S. calcicola, S. candida, S. caprea, S. caroliniana, S. cascadensis, S. chamissonis, S. chlorolepis, S. cinerea, S. columbiana, S. commutata, S. cordata, S. daphnoides, S. delnortensis, S. discolor, S. drummondiana, S. eastwoodiae, S. elaeagnos, S. eriocephala, S. euxina, S. exigua, S. famelica, S. farriae, S. floridana, S. fuscescens, S. geyeriana, S. glauca, S. gooddingii, S. hastata, S. herbacea, S. hookeriana, S. humboldtiana, S. humilis, S. interior, S. irrorata, S. jejuna, S. jepsonii, S. laevigata, S. lasiandra, S. lasiolepis, S. lemmonii, S. ligulifolia, S. lucida, S. lutea, S. maccalliana, S. melanopsis, S. monochroma, S. monticola, S. myricoides, S. myrsinifolia, S. myrtillifolia, S. nigra, S. niphoclada, S. nivalis, S. nummularia, S. orestera, S. ovalifolia, S. pedicellaris, S. pellita, S. pentandra, S. petrophila, S. phlebophylla, S. planifolia, S. polaris, S. prolixa, S. pseudomonticola, S. pseudomyrsinites, S. pulchra, S. purpurea, S. pyrifolia, S. raupii, S. reticulata, S. richardsonii, S. rotundifolia, S. scouleriana, S. sericea, S. serissima, S. sessilifolia, S. setchelliana, S. silicicola, S. sitchensis, S. sphenophylla, S. stolonifera, S. taxifolia, S. thurberi, S. tracyi, S. triandra, S. turnorii, S. tweedyi, S. tyrrellii, S. uva-ursi, S. vestita, S. viminalis, S. wolfii, S. ×fragilis, S. ×jesupii, S. ×pendulina, S. ×sepulcralis, S. ×smithiana
Subordinate taxa
S. rotundifolia var. dodgeana, S. rotundifolia var. rotundifolia
Synonyms S. gracilis, S. gracilis var. textoris, S. petiolaris var. gracilis, S. ×subsericea
Name authority Trautvetter: Nouv. Mém. Soc. Imp. Naturalistes Moscou 2: 304, plate 11. (1832) Smith: Trans. Linn. Soc. 6: 122. (1802)
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