Download PDF
Salix
alba L.
Standardized Common
Name: White Willow
Family: Salicaceae
Taxonomy: There are over 500
species of Salix, mostly native to cold or temperate parts of the
Northern Hemisphere. The taxonomy of the genus is therefore complicated, with
numerous sections recognized. Salix alba is classified in Subg. Salix,
Sect. Salix, along with species such as S. fragilis L. (Brittle
Willow) and S. babylonica L. (Weeping Willow). It has been reported to
hybridize with these and other species, including S. nigra Marsh. (Black
Willow) and S. lucida Muhl. (Pacific Willow). It is a native of Eurasia
and is widely naturalized in eastern North America.
Description: Tree to 25 m high,
with short trunk and ascending, spreading crown; bark grayish, irregularly
ridged or fissured; twigs thin and flexible, often hanging downward, olive to
brown or reddish brown, soft-pubescent. Leaves alternate, petiolate, narrowly
lanceolate to lanceolate or narrowly oblong, 4–13 cm long; base attenuate to
cuneate; apex acute to long-acuminate; margins minutely serrate; upper surface
grayish-green, lower surface whitish; young leaves softly pubescent on both
surfaces, becoming nearly glabrous at maturity especially above. Flowers
minute, unisexual, borne in unisexual catkins 3–5 cm long, each flower
subtended by a scale. Perianth absent; male flowers consist of 2 stamens,
female flowers of an ovary with 2–4 stigmas. Fruit a capsule, 3–5 mm long,
1-loculed, 2–4 valved; seeds numerous, with long downy hair.
Parts
in Commerce:
Bark, primarily from 2–3-year-old branches, or young twigs
Identification:
- Pieces from
small branches channeled, 1–2 cm broad; larger pieces nearly flat
- 1–2(–3) mm thick
- Outer surface
greenish to grayish brown; young bark smooth, old bark dull, slightly
wrinkled and sometimes dark brown
- Inner surface
pale reddish or cinnamon, longitudinally striated to nearly smooth
- Fracture short
in outer portion, coarsely fibrous in inner portion
- Cork very thin,
brown; cortex and secondary phloem reddish to cinnamon-colored, sometimes
appearing multilayered, sometimes separating irregularly into fibrous
layers especially in small pieces
- Phloem in
transverse section contains many thin interrupted layers of fiber cells;
this may be visible (with a dissecting scope) on a moistened cut surface
as lines of tiny, elongated, slightly darker spots broken into segments by
very narrow, slightly paler perpendicular rays
- Young twigs, if
included, have whitish xylem
- Sometimes has
weak aromatic odor
- Taste
astringent, slightly bitter
Adulterants: Numerous other
species of willow are used medicinally, including those mentioned above, S.
purpurea L. (Purple Willow), and S. daphnoides Vill. (Violet
Willow). Some of these could be confused with S. alba in the wild.
According to European authorities, all species of acceptable chemical content
(which will have a similar taste) may be sold collectively as “willow bark.”
Indeed, many species are more potent than S. alba in terms of salicin
content. In the United States, Herbs of Commerce specifies that each
such species should be sold under a different common name. Distinguishing among
some of these species with certainty, given only the bark, may be possible only
by chemical fingerprinting (assuming that reliable differences among species
can be found). Some useful microanatomical features have been identified; for
example, unlike many of the commercially valuable species, S. alba has
stone cells only in the cortex, not in the phloem. However, it seems unlikely
that numerous closely related species of Salix could be adequately
differentiated through bark anatomy alone.
References:
Argus GW. The Genus Salix in the Southeastern
United States. Ann Arbor, MI: American Society of Plant Taxonomists; 1986.
Systematic Botany Monographs, vol. 9.
Argus GW. Infrageneric Classification of Salix
(Salicaceae) in the New World. Ann Arbor, MI: American Society of Plant
Taxonomists; 1997. Systematic Botany Monographs, vol. 52.
British Herbal Pharmacopoeia, p. 188.
Elias TS. The Complete Trees of North America.
Field Guide and Natural History. New York, NY: Gramercy Publishing Co.;
1987.
Fang Z, Zhao S, Raven PH. Salicaceae. In: Wu Z-Y,
Raven PH, eds. Flora of China, vol. 4. Cycadaceae through Fagaceae.
Beijing: Science Press and St. Louis, MO: Missouri Botanical Garden Press;
1999:139–275.
Fernald ML. Gray’s Manual of Botany, 8th ed. New York: American Book
Company; 1950:488–519.
Greenish HG. Materia Medica. Jodhpur: Scientific Publishers (India); 1920
reprinted 1999:285–287.
Rechinger KH, rev. Akeroyd JR. Salix. In: Tutin TG, Heywood VH, Burges NA, et al.,
eds. Flora Europaea. 2nd ed., vol. 1. Cambridge:
Cambridge University Press; 1993:53–64.
Triest L. Hybridization in staminate and pistillate Salix
alba and S. fragilis (Salicaceae): morphology versus RAPDs. Pl
Syst Evol. 2001;226:143–154.
Wichtl M, ed. Herbal Drugs and
Phytopharmaceuticals, 3rd English
ed. Stuttgart: medpharm Scientific Publishers and Boca Raton, FL: CRC Press;
2004:534–537.
Youngken HW. Text-Book of Pharmacognosy, 5th ed. Philadelphia, PA: The
Blakiston Company; 1943:250–251.
|
|