Salix bebbiana
Salix ×fragilis
beak willow, Bebb willow, Bebb's willow, gray or Bebb's or long-beak willow, gray willow, grey willow, long-beak willow
brittle willow, crack willow, hybrid white willow
branches divaricate, sometimes ± brittle at base, yellow-brown to dark red-brown, not or weakly glaucous, pilose to glabrescent, peeled wood often with very dense striae, to 25 mm;
branchlets yellow-green or red-brown, moderately to very densely villous to glabrescent.
stipules rudimentary or absent on early ones, apex acute, acuminate, or convex;
petiole convex to flat adaxially, 2–5.5–13 mm, pubescent adaxially;
largest medial blade narrowly oblong, narrowly elliptic, elliptic, oblanceolate, or obovate, 20–44–87 × 10–16–45 mm, base cuneate, convex, or rounded, margins flat, entire, crenate, or irregularly serrate, glands submarginal, apex acute, acuminate, or convex, abaxial surface glaucous, moderately densely pubescent or long-silky to glabrescent, hairs white or gray, wavy, adaxial finely impressed-reticulate, dull or slightly glossy, moderately densely pubescent, sparsely short-silky, or glabrescent, hairs white or gray;
proximal blade margins entire, gland-dotted;
juvenile blade yellowish green or reddish, pilose or sparsely to moderately densely tomentose or long-silky abaxially, hairs white.
adaxial nectary oblong or ovate, 0.3–0.8 mm;
filaments distinct or connate less than 1/2 their lengths, glabrous or hairy on proximal 1/2;
anthers yellow or purple turning yellow, ellipsoid or shortly cylindrical, 0.5–0.8 mm.
adaxial nectary oblong or square, 0.3–0.8 mm;
ovary obclavate, beak slightly bulged below styles (long-beaked);
ovules 6–16 per ovary;
styles 0.1–0.4 mm;
stigmas slenderly to broadly cylindrical.
5–9 mm.
staminate flowering just before leaves emerge, pistillate flowering as leaves emerge; staminate stout to globose, 10–42 × 7–16 mm, flowering branchlet 0.5–11 mm; pistillate loosely flowered, stout, slender, or subglobose, 16.5–85 × 9–32 mm, flowering branchlet 1–26 mm;
floral bract tawny, 1.2–3.2 mm, apex rounded, abaxially hairy to glabrescent, hairs straight or wavy.
×fragilis Linnaeus: The hybrid white willow, S. alba Linnaeus × S. euxina I.
, a European introduction, is the most commonly cultivated and naturalized tree-willow in the flora area.
is characterized by: trees, 3–20 m, stems erect or drooping;
branches highly brittle at base;
petioles with spherical or foliaceous glands distally, pilose or villous adaxially;
largest medial leaf blade amphistomatous, very narrowly elliptic or narrowly elliptic, margins uniformly serrate or serrulate, abaxial surface glaucous, both surfaces sparsely long-silky to glabrescent, adaxial surface slightly glossy or dull;
juvenile leaves at first densely long-silky soon glabrous; pistillate bract deciduous after flowering;
stamens 2;
anthers yellow; pistillate adaxial nectary shorter than or equal to stipe;
stipe 0.3–0.5 mm;
ovary pyriform, glabrous;
ovules 6–12 per ovary;
styles 0.4–1 mm;
capsules 4.5–6 mm; 2n = 57, 76.
= 38.
Salix bebbiana
Salix ×fragilis
Salix bebbiana occurs in Nunavut on Akimiski Island in James Bay.
Hybrids:
Salix bebbiana forms natural hybrids with S. candida, S. geyeriana, S. humilis, and S. petiolaris. Reports of hybrids with S. discolor (C. K. Schneider 1921; M. L. Fernald 1950) are not based on convincing specimens, and synthetic hybrids could not be made (G. W. Argus 1974). Reports of hybrids with S. eriocephala and S. myricoides (Fernald) are unverified. Controlled pollinations with S. eriocephala and S. interior had low seed viability (A. Mosseler 1990).
Salix bebbiana × S. candida (S. ×cryptodonta Fernald, as species) is intermediate between parental species. It resembles S. candida in having juvenile leaves densely woolly, mature leaves sparsely to moderately woolly abaxially, margins strongly revolute to crenulate, and ovaries woolly; and S. bebbiana in having stipes 2.8–3 mm and capsules long-beaked, 8–9 mm. The hybrid commonly occurs in Newfoundland.
Salix bebbiana × S. geyeriana: A plant with the pistillate catkins and flowers of S. bebbiana and the narrow, entire or slightly serrulate leaves with white and ferruginous hairs of S. geyeriana was collected by R. D. Dorn in a mixed population in Montana (Beaverhead County).
Salix bebbiana × S. humilis: Reported by C. K. Schneider (1921) and M. L. Fernald (1950) and successfully synthesized by G. W. Argus (1974, 1986).
Salix bebbiana × S. petiolaris is known from Ontario, based on an infertile pistillate specimen, and from Alberta and Saskatchewan, where it is relatively uncommon. It was successfully synthesized (G. W. Argus 1974, 1986) and controlled pollinations showed high seed viability (A. Mosseler 1990).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Individual trees can persist for years by trunk suckering and spread vegetatively by shoot fragmentation along stream margins, shingle and sand beaches, sedge meadows, hardwood forests, and sand pits.
A study of Salix ×fragilis in Colorado (as S. ×rubens) showed that 2172 of 2175 trees were pistillate. Occasionally seed was set, possibly fertilized by S. alba (P. B. Shafroth et al. 1994). There are at least five clones of S. ×fragilis (as S. ×rubens) in cultivation (T. Berg in B. Jonsell and T. Karlsson 2000+, vol. 1); the pistillate are sterile but the staminate produce viable pollen. The hybrid plants are often misidentified as S. “fragilis” or as S. nigra. In the flora area, reproduction of the hybrid seems to be mainly by stem fragmentation.
Prior to the lectotypification of Salix fragilis Linnaeus and the description of S. euxina (I. V. Belyaeva 2009), the name S. “fragilis” was often inadvertently used for both the pure species and for its hybrids with S. alba. Thus all herbarium specimens under the names “fragilis” and “×rubens” need to be revised.
Salix ×fragilis can be separated from S. euxina by having branches and branchlets hairy or glabrescent in age versus glabrous; leaf blades not glaucous abaxially versus glaucous; leaves amphistomatous versus hypostomatous or with stomata only along veins and at apex; and pistillate catkins slender and loosely flowered versus stout and moderately densely flowered.
Several molecular studies have been designed to understand the nature of this hybrid. H. Beissmann et al. (1997), using AFLP markers, were able to recognize three clusters: Salix alba, S. euxina (as S. fragilis), and S. ×fragilis (as S. ×rubens); but a study by K. De Cock et al. (2003), also using AFLP markers, was unable to resolve S. alba and S. ×fragilis (as S. ×rubens). They recommended the use of experimental hybridization to study the genesis of this hybrid. Molecular and genetic studies by L. L. Triest (2001) and coworkers concluded that in modern open agricultural situations in Belgium, hybridization was of low occurrence, and that morphologically intermediate plants were not necessarily genetically intermediate. These studies saw different facets of the question. Clearly there are three entities, S. alba, S. euxina, and their hybrid but, because S. euxina may be rare outside of cultivation, natural hybridization may not occur and the question of whether S. ×fragilis can be backcrossed with S. alba remains to be studied. The specimens used in these molecular studies require reidentification.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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