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).