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Published In: Species Plantarum 2: 1021–1022. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library

Project Name Data (Last Modified On 9/22/2017)
Acceptance : Accepted
Project Data     (Last Modified On 7/9/2009)
Status: Introduced


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1. Salix alba L. (white willow)

S. alba var. caerulea (Sm.) Sm.

S. alba var. calva G. Mey.

S. alba var. vitellina (L.) Stokes

Pl. 554 d–g; Map 2573

Plants medium to large trees, 10–25 m tall, usually not reproducing clonally. Trunks with the bark becoming deeply ridged and furrowed, brown to grayish brown. Branches flexible to somewhat brittle at the base, yellowish, grayish, or reddish brown. Branchlets yellowish or grayish to reddish brown, not glaucous, sparsely to occasionally densely pubescent with short to long, curved or spreading, sometimes silky hairs. Winter buds blunt at the tip, the scale margins fused. Leaves alternate. Petioles 3–13 mm long, with paired or clustered glandular dots, or stalked glands toward the tip, the upper side hairy. Stipules minute to well-developed, sharply pointed at the tip. Leaf blades 6–12 cm long, 4–8 times as long as wide, narrowly oblong to elliptic or lanceolate, usually tapered to a sharply pointed tip, angled or tapered at the base, the margins flat, sharply toothed, the upper surface dull, sparsely hairy to nearly glabrous, the undersurface glaucous, sparsely to densely pubescent with long, white, silky, appressed hairs. Catkins flowering as the leaves appear, on distinct, leafy, flowering branchlets; the bracts 1.5–2.8 mm long, entire, rounded at the tip, tawny, glabrous or sparsely and evenly hairy, those of the pistillate catkins not persistent at fruiting; the staminate catkins 2.5–6.0 cm long; the pistillate catkins 3–5 cm long. Staminate flowers with 2 stamens, the filaments free, hairy toward the base; nectaries 2, free. Pistillate flowers with the styles fused nearly to the tip, the stigmas flat or broadly cylindric; nectary 1. Fruits 3.5–5.0 mm long, on stalks 0.2–0.8 mm long. 2n=76. April–May

Introduced, scattered widely in the state, most commonly in the western half (native of Europe, Asia; introduced widely in the U.S. [including Alaska and Hawaii], except for most of the Great Plains; also Canada). Banks of streams, margins of ponds, and edges of bottomland prairies; also moist disturbed areas.

White willow is an attractive, often large cultivated tree that escapes sporadically. Traditionally, several infraspecific taxa were recognized within S. alba (Steyermark, 1963). However, several authors, including Argus (1986), have treated all of these as cultivars (horticulturally developed variants). Of these, plants referred to as var. vitellina, which are characterized by erect to slightly pendant, yellowish brown, sparsely hairy branches, often are planted and occasionally may escape

Weeping willow, S. babylonica L. was treated by Steyermark (1963) as having become established outside of cultivation in Dent and Jackson Counties. He noted, however, that true S. babylonica is cold-hardy only in the southern third of the United States. Argus (1986, 2007) similarly mapped its range outside cultivation as occurring to the south of Missouri, and the species thus has been excluded from the Missouri flora. It should be noted that a few historical specimens document its cultivation in the St. Louis region in the 1830s, but there is no information on how successful such trees were during that era. Argus (1986) noted that plants growing farther north in the United States mostly represent a horticultural hybrid between S. alba and S. babylonica known as S. ×sepulcralis Simonk. (Pl. 554 h, i). This hybrid differs from S. babylonica in its usually hairy branches, slender pistillate catkins (2.8–4.8 times longer than wide) that are borne on noticeably elongate (3–14 mm) lateral branches, ovaries pear-shaped, and capsules 1–2 mm long. In contrast, true S. babylonica has glabrous branches, relatively stout pistillate catkins (1.3–2.2 times as long as wide) that are borne on at most short (to 4 mm) branches, ovaries egg- or turnip-shaped, and capsules 2.0–2.7 mm. Salix ×sepulcralis has been collected in the wild sporadically, primarily in the eastern portion of the state.

A second weeping willow that is less commonly cultivated in Missouri, S. ×pendulina Wender., arose as a horticultural hybrid between S. babylonica and S. euxina J. Belyaeva (see the discussion of S. ×fragilis below). It is morphologically very similar to S. ×sepulcralis, but differs in its more coarsely toothed leaves, its relatively loosely flowered staminate catkins, and in its fused, more or less cup-shaped staminate nectaries (vs. 2 free staminate nectaries in S. ×sepulcralis). In Missouri, S. ×pendulina is known as an apparent escape thus far only from historical specimens from Jasper and Marion Counties.

Another horticulturally derived hybrid with ascending (nonweeping) branches that has escaped sporadically in Missouri is S. ×fragilis L. (S. alba × S. euxina; Pl. 555 a–c) This hybrid was long known by the name S. ×rubens Shrank, but a recently approved proposal to conserve the type of the name S. fragilis based upon a specimen of the hybrid necessitates the name change (Belyaeva, 2009; Argus, 2010). True crack willow, which recently was renamed S. euxina (Belyaeva, 2009), is a western Asian species that is widely cultivated in Europe and occasionally also in North America, where it rarely if ever escapes (Argus, 2007). The Russian willow specialist, A. K. Skvortsov (1973), stated that all of the crack willow specimens collected in North America that he had examined turned out to represent the hybrid, rather than the parent. This hybrid was treated under the name S. fragilis by Steyermark (1963). It was first reported from Missouri as a hybrid by Mühlenbach (1983, as S. ×rubens). It differs from S. alba in having mature leaves glabrous (vs. densely long-silky-hairy), petioles sparsely hairy (vs. densely long-silky-hairy), branches highly brittle at the base (vs. flexible or only somewhat brittle), styles 0.4–1.0 mm (vs. 0.2–0.4 mm) long, and ovaries tapering to the styles (vs. slightly bulged below the styles).



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