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.)

Salix eastwoodiae and S. commutata are distinct species with different ploidal levels, the former tetraploid and the latter diploid; where they come into contact in the Pacific Northwest, hybrids occur and vegetative plants are often difficult to separate. See comparison below. The most important difference is that ovaries of S. eastwoodiae usually are silky turning glabrescent in age and those of S. commutata are glabrous. Populations occur in Oregon with both glabrous and hairy ovaries without any other evident differences. There are also unusual specimens, which are often tentatively identified as S. eastwoodiae, that have glabrous ovaries and patches of hairs at the base and on the sutures. The possibility that they are hybrids between S. eastwoodiae and S. boothii, S. commutata, or S. lemmonii needs study.

Salix commutata is distinguished from S. eastwoodiae by having leaf blades sometimes amphistomatous, 1.5–3.4 times as long as wide, teeth 0–19 per cm, adaxial surfaces glabrous or pilose to villous, floral bracts tawny to brown, staminate and pistillate adaxial nectaries oblong to square, and ovaries glabrous; S. eastwoodiae has leaf blades hypostomatous, 1.8–5 times as long as wide, teeth 0–10 per cm, adaxial surfaces tomentose or long-silky, floral bracts brown to black, staminate and pistillate adaxial nectaries narrowly oblong to oblong, and ovaries silky to glabrescent.

Hybrids:

Salix eastwoodiae forms natural hybrids with S. arizonica, S. boothii, and S. commutata.

Salix eastwoodiae × S. lasiandra was found in Sierra County, California, growing with both parents in a wetland along a disturbed roadside. It had leaf indumentum and hair color of S. eastwoodiae and leaf shape and margins of S. lasiandra. Catkins of this intersubgeneric hybrid were teratological and presumably infertile.

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