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least willow, round-leaf willow

Tracy's willow

Habit Plants 0.005–0.05 m, (dwarf), forming clones by rhizomes. Shrubs, 1–6 m. Stems: branches gray-brown to red-brown, strongly to weakly glaucous, glabrous; branchlets yellow-brown to red-brown, (weakly glaucous), glabrous or sparsely to moderately densely velvety or tomentose.
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 absent, rudimentary, or foliaceous on early ones, foliaceous on late ones, (2.5–9 mm), apex rounded or convex;

petiole convex to flat, or shallowly grooved adaxially, 5–11 mm, tomentose or velvety adaxially;

largest medial blade lorate, oblanceolate, or elliptic, 55–96 × 15–34 mm, 2–3.7 times as long as wide, base convex, margins slightly revolute, entire, sinuate or serrulate, apex acuminate to acute, abaxial surface glaucous, sparsely pubescent to moderately densely tomentose or glabrous, hairs (white, sometimes also ferruginous), straight or curved, adaxial slightly glossy, sparsely tomentose to glabrescent;

proximal blade margins entire or serrulate;

juvenile blade reddish, very densely tomentose or puberulent to glabrescent 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 narrowly oblong, oblong, or ovate, 0.3–0.8 mm;

filaments connate less to more than 1/2 their lengths;

anthers purple turning yellow, ellipsoid, shortly cylindrical, or globose, 0.36–0.44 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, or narrowly oblong to flask-shaped, 0.2–0.6 mm;

stipe 1–1.7(–2.4) mm;

ovary pyriform, beak sometimes slightly bulged below styles;

ovules 12 per ovary;

styles 0.1–0.6 mm;

stigmas flat, abaxially non-papillate with rounded or pointed tip, 0.1–0.3 mm.

Capsules

3.8–8.3 mm.

2.4–3.6 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 or just before leaves emerge; staminate stout, 17–30 × 7–9 mm, flowering branchlet 1.5–5 mm; pistillate very densely flowered, stout to slender, 17–42 × 6–11 mm, flowering branchlet 1.5–3 mm;

floral bract brown or bicolor, 0.8–1.6 mm, apex rounded to truncate, abaxially hairy throughout or proximally, hairs wavy or straight.

Salix rotundifolia

Salix tracyi

Phenology Flowering early Apr-early May.
Habitat Shores and floodplains, sandy, gravelly, or rocky substrates, often serpentine
Elevation 90-500 m (300-1600 ft)
Distribution
from FNA
AK; MT; WY; NT; YT; e Asia
[WildflowerSearch map]
[BONAP county map]
from FNA
CA; OR
[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.)

Ball described Salix tracyi as part of a group of “more or less localized endemic willows of northern California and southern Oregon.” A. K. Skvortsov (1971), followed by G. W. Argus (1993), thought that this species was a stunted form, perhaps shade-growth, of S. lasiolepis. R. D. Dorn (2000) studied the taxon in the field and considered it to be a distinct species. He noted that it could “usually” be separated from S. lasiolepis by its shorter styles, longer stipes, less hairy floral bracts, shorter catkins, thinner, less hairy leaves, and reddish juvenile leaves. He also noted differences in flowering times but they overlap completely. The differences are subtle and, although not diagnostic, should be studied further. Salix tracyi is treated here as a species because of its relatively large, localized range and interesting biological and morphological characteristics. Local botanists making collections from tagged individuals could provide useful information on habitat, elevation, flowering time, and morphology. Experimental study of this and the other serpentine endemic Salix in the region (see also 110. S. breweri and 111. S. delnortensis) could provide insights into their evolution and their relationship with S. lasiolepis.

A numerical taxonomic study by T. J. Crovello (1968) found that Salix tracyi clustered with members of sect. Cordatae, but both G. W. Argus (1997) and R. D. Dorn (2000) placed it in sect. Mexicanae with S. lasiolepis.

(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. 156.
Parent taxa Salicaceae > Salix > subg. Chamaetia > sect. Herbella Salicaceae > Salix > subg. Vetrix > sect. Mexicanae
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. 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. rotundifolia, S. scouleriana, S. sericea, S. serissima, S. sessilifolia, S. setchelliana, S. silicicola, S. sitchensis, S. sphenophylla, S. stolonifera, S. taxifolia, S. thurberi, 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
Name authority Trautvetter: Nouv. Mém. Soc. Imp. Naturalistes Moscou 2: 304, plate 11. (1832) C. R. Ball: Univ. Calif. Publ. Bot. 17: 403, plates 69, 70. (1934)
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