Flora of North America species comparison

Little is known about the origin of the strongly weeping cultivar of Salix babylonica. It was described by Linnaeus (1737[1738]) based on young garden specimens (W. J. Bean 1970–1988, vol. 4). It is thought to have originated in China, although it no longer occurs in the wild and its origin is uncertain. Selections are thought to have been transported to Europe along the trade route from China. In Tajikistan, there are three cultivated clones, one of which is staminate (A. K. Skvortsov 1999). Taxonomic treatments of S. babylonica are variable. Some botanists recognize a single species, including both pendulous and non-pendulous forms (Skvortsov), while others recognize four species: S. babylonica, with a weeping habit, S. capitata Y. L. Chou & Skvortsov, S. pseudolasiogyne H. Léveillé, and the commonly cultivated S. matsudana Koidzumi (Fang Z. F. et al. 1999), with an erect or spreading habit. Here, S. babylonica is treated in a narrow sense, including only weeping forms.

Salix babylonica is not cold tolerant and is not commonly grown in Europe (R. D. Meikle 1984) or in northern North America. In the flora area, cultivated trees with strongly pendulous branches and branchlets have been identified as S. babylonica (G. W. Argus 1985, 1986, 1993), but many are hybrids with S. alba (S. ×sepulcralis) or S. euxina (S. ×pendulina). Salix ×sepulcralis, especially nothovar. chrysocoma, with bright yellow branchlets, is the most commonly grown of these hybrids. All reported occurrences of S. babylonica need verification.

Hybrids:

Salix ×sepulcralis Simonkai: Weeping willow, S. alba × S. babylonica, is introduced from Europe and widely naturalized throughout the world. Synonyms include S. ×salamonii Carrière ex Henry and S. ×sepulcralis nothovar. chrysocoma (Dode) Meikle. It is characterized by: trees, to 12 m, stems pendulous; branches somewhat to highly brittle at base, yellowish, yellow-green, or yellow-brown; branchlets yellowish, yellow-green, or golden; stipules rudimentary or foliaceous on late leaves; petiole not glandular or with pairs or clusters of spherical glands distally or scattered throughout, short-silky adaxially; largest medial blade amphistomatous or hemiamphistomatous, narrowly elliptic to very narrowly so, margins finely serrulate or spinulose-serrulate, abaxial surface glaucous, adaxial glaucous, sparsely long-silky to glabrescent, hairs white or white and ferruginous, adaxial surface slightly glossy; catkins on distinct flowering branchlet 3–14 mm; staminate moderately densely flowered, slender, 23–53 × 3–9 mm; pistillate moderately densely to loosely flowered, slender to stout, 18–30 × 3–8 mm, flowering branchlet 3–14 mm; pistillate bracts persistent after flowering; staminate abaxial and adaxial nectaries distinct; stamens 2; anthers 0.5–0.8 mm; pistillate nectary longer than stipe; stipe 0–0.2 mm; ovaries gradually tapering to styles; ovules 4 per ovary; styles 0.15–2 mm; capsules 1–2 mm. In the flora area, it occurs in: British Columbia, New Brunswick, Nova Scotia, Ontario, Quebec; Alaska, Arizona, Arkansas, California, Connecticut, District of Columbia, Illinois, Iowa, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Missouri, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, Ohio, Oregon, Pennsylvania, Tennessee, Utah, Virginia, and West Virginia.

The most commonly cultivated, and sometimes escaped, weeping willow with golden or yellow-green branchlets is Salix ×sepulcralis nothovar. chrysocoma (Dode) Meikle. It probably originated as S. alba var. vitellina × S. babylonica (R. D. Meikle 1984). According to F. S. Santamour Jr. and A. J. McArdle (1988), S. ×sepulcralis cv. Salamonii has a broadly pyramidal crown and is only slightly pendulous. It is not clear just how this cultivar differs from S. ×pendulina. For a discussion of the taxonomy of these and other weeping willows see J. Chmela (1983).

Salix ×pendulina Wenderoth: Weeping willow, S. babylonica × S. euxina, is introduced from Europe and grown throughout the world. It is characterized by: trees, 2.5–12 m, stems pendulous; branches highly brittle at base, yellow-brown, gray-brown, or red-brown; branchlets yellowish to brownish; stipules foliaceous on late leaves; petioles glabrous, pilose, or velvety to glabrescent adaxially; largest medial blade amphistomatous or hypostomatous, very narrowly elliptic to lanceolate, or linear, margins serrulate, irregularly so, or spinulose-serrulate, abaxial surface glaucous, adaxial slightly glossy or dull; catkins on distinct flowering branchlet, 3–14 mm; staminate loosely flowered, stout, 16–34 × 7–11 mm; pistillate densely or moderately densely flowered, slender or stout, 20–36 × 3.5–11 mm; pistillate bract persistent after flowering; staminate abaxial and adaxial nectaries connate and shallowly cup-shaped; stamens 2; anthers 0.5–0.6 mm; pistillate nectary longer than stipe; stipe 0 mm; styles 0.2–0.6 mm; ovules 4–8 per ovary; capsules 1.8–3.5 mm. In the flora area, it occurs in: Ontario; California, Connecticut, District of Columbia, Georgia, Illinois, Indiana, Maine, Maryland, Massachusetts, Michigan, Missouri, Nebraska, New Jersey, New Mexico, New York, North Carolina, Ohio, Oregon, Pennsylvania, Texas, Virginia, Washington, and West Virginia.

Reports of this hybrid in British Columbia and California are undocumented. Plants of Salix ×pendulina with prominent, caudate stipules are var. blanda (Andersson) Meikle; those with ovaries with patchy or streaky hairiness are var. elegantissima (K. Koch) Meikle.

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

Vegetative specimens of Salix hastata often are misidentified as S. barclayi. The characters that indicate S. hastata, or sometimes possible hybrids, are the presence of ferruginous hairs on juvenile leaves or adaxial midribs of mature leaves, leaf margins often entire or with teeth present only distally, and buds with inner membranaceous layer not separating from outer layer.

Salix barclayi is distinguished from S. farriae and S. hastata by having bud-scales with inner membranaceous layer separating from outer layer, juvenile blades glabrous, pilose, or moderately densely villous, largest medial blades oblong, narrowly elliptic, elliptic, oblanceolate, or obovate, margins always toothed, pistillate flowering branchlets 4–24 mm, staminate flowering branchlets 0–17 mm, floral bracts brown to black, moderately densely hairy, anthers 0.6–1 mm, styles 0.6–2.5 mm, and stipes 0.4–1.5 mm; S. farriae has bud-scales with inner membranaceous layer separating from outer layer, juvenile blades glabrous or sparsely villous, largest medial blades narrowly elliptic to elliptic, margins usually entire, pistillate flowering branchlets 1.5–14 mm, staminate flowering branchlets 1–5 mm, floral bracts bicolor, brown, or black, sparsely hairy, anthers 0.3–0.6 mm, styles 0.3–1.2 mm, and stipes 0.5–1.2 mm; and S. hastata has bud-scales with inner membranaceous layer not separating from outer layer, juvenile blades sparsely pubescent, largest medial blades narrowly to broadly elliptic, narrowly ovate, or ovate, margins usually entire, pistillate flowering branchlets 1.5–9 mm, staminate flowering branchlets 1–7 mm, floral bracts brown or bicolor, sparsely hairy, anthers 0.4–0.6 mm, styles 0.2–0.48 mm, and stipes 0.4–1.2 mm.

Hybrids:

Salix barclayi is morphologically highly variable. While it is possible that much of this variability is inherent, hybridization and introgression have played an important role.

Salix barclayi forms natural hybrids with S. arctica, S. barrattiana, S. brachycarpa, S. cascadensis, S. commutata, S. farriae, S. hastata, S. hookeriana, S. richardsonii, and S. stolonifera.

Salix barclayi × S. barrattiana is characterized by oily buds that stain the pressing paper yellow, and leaves often entire, or nearly so, and closely gland-dotted, and not glaucous abaxially. Some hybrids resemble S. barclayi in having ovaries glabrous and leaves serrulate and slightly glaucous abaxially, while others resemble S. barrattiana in having stipules marcescent and leaves short-hairy on both surfaces and not glaucous abaxially, but it is the presence of the oily buds characteristic of S. barrattiana that indicates their hybridity. The hybrids usually were from populations that included both parents. An important ramification of the discovery of this hybrid is that the specimen on which the chromosome number for S. barclayi (R. D. Dorn 1976) is based is a plant with oily buds, which has leaves with a mixture of weakly developed teeth and closely gland-dotted, entire margins, and is putatively identified as this hybrid. Further chromosome counts for S. barclayi are needed. Hybrids are known in British Columbia from the mountains in the Peace and Liard river basins, and in Mt. Robson National Park. The hybrid should be suspected wherever the parents occur together.

Salix barclayi × S. cascadensis, collected in Washington in alpine mats growing with both parents, has ovaries with hairy beaks indicating hybridization.

Salix barclayi × S. commutata resembles S. barclayi in having leaves glaucous abaxially, and S. commutata in having leaves hairy on both surfaces (northern British Columbia, Unalaska Island, and southeastern Alaska).

Salix barclayi × S. farriae is represented by a series of specimens resembling S. barclayi but with ferruginous hairs on juvenile leaves or on adaxial midribs of mature leaves, found from the Rocky Mountains of Alberta to southern Yukon and adjacent Northwest Territories. Similar specimens from Alaska may be the hybrid S. barclayi × S. hastata. Both of these hybrids require further study. See 63. S. hastata and 64. S. farriae.

Salix barclayi × S. hookeriana hybrids or introgressants at Tanis Lake, Alaska, have subentire leaves and stipes glabrous or hairy.

Salix barclayi × S. richardsonii hybrids and intergrades are relatively common in Alaska, British Columbia, and Yukon. They resemble S. barclayi in having catkins borne on distinct flowering branchlets, small stipules, anthers yellow and longer, and S. richardsonii in having marcescent stipules, branchlets and branches coarsely villous with spreading hairs, pistillate nectaries longer than stipes, and catkins sometimes on relatively short flowering branchlets.

Salix barclayi × S. scouleriana has the general appearance of S. barclayi but the densely hairy ovaries and the relatively long stigmas (0.9–0.92 mm) of S. scouleriana. It was growing with S. barclayi in openings created in white spruce by bark beetles.

Salix barclayi × S. stolonifera is characterized by relatively small leaves with irregularly serrulate margins, some young leaves reddish green, and a prostrate habit (G. W. Argus 1973).

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