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Dioscorea
villosa L.
Standardized Common
Name: Wild
Yam
Other Common Names: Colic Root, North
American Wild Yam, Rattlebox, Rheumatism Root
Family: Dioscoreaceae
Taxonomy: Dioscorea,
the yam genus, includes about 850 species of tropical and subtropical vines. In
the broad sense, D. villosa includes all of the native wild yams of the
United States except the southeastern D. floridana Bartlett. Most
authors in recent decades divide it into two species, D. villosa and D.
quaternata J. F. Gmel., but authors differ on which of these is the common
and widespread plant. The different forms are correlated with different
habitats (lowland bogs versus rocky hilltops) and a whole range of intermediates
is found; thus any division into two species is somewhat arbitrary. On the
other hand, a few authorities subsume D. floridana into D. villosa
as D. villosa var. floridana (Bartlett) H. E. Ahles, despite
consistent morphological differences that do appear to warrant its preservation
as a separate species.
Description: Rhizomatous
perennial herb. Rhizomes long, 0.5–2.0 cm in diameter, unbranched to crowded
with short branches, brownish, with cup-shaped stem scars hardly elevated from
surface. Stems climbing, twining upward from right to left, terete to narrowly
winged or polygonal. Leaves alternate or whorled below, alternate above,
long-petioled, cordate, 3–13 cm long, breadth about equaling length; base
cordate or with basal lobes truncate; apex acuminate or acute, sometimes bent;
margins entire or slightly undulate; main veins usually 9–11, arcuate;
pubescence variable, occasionally glaucous. Inflorescences unisexual, solitary,
cymose; male cymes 1–3-flowered, female cymes 4–18-flowered. Flowers greenish
white; perianth usually rotate-campanulate, with 6 tepals; male flowers 1–3 mm
in diameter, female flowers 2–4 mm in diameter; stamens or staminodes 6; ovary
inferior, style branches 2. Fruit a capsule, ovate to obovate or obreniform,
1–3.5 cm broad, 3-winged, flattened; seeds 2 per locule.
Parts
in Commerce:
Rhizome
Identification:
- Long, seldom
branched pieces or knotty contorted pieces with frequent short branches,
0.5–2.0 cm thick
- Branching
laterally
- Not jointed at
nodes
- Slightly
flattened to cylindrical
- Outer surface
pale brown to yellowish brown, not strongly yellow, and rough; inside
whitish to yellowish
- Upper surface
with small circular stem scars, not raised much above surface
- Lower surface
with numerous slender, tough roots or sharp projections where roots were
present
- Fracture very
tough
- In
cross-section, has thin yellow epidermis; narrow cortex; broad stele
consisting of pale starchy parenchyma with numerous scattered, small,
yellowish vascular bundles
- Taste at first
starchy and tasteless, then somewhat bitter or acrid
Adulterants: The other native
species of Dioscorea in the United States, D. floridana, may
easily be confused with D. villosa, though its range is limited. This
species has rhizomes with articulated nodes; each node bears a deciduous scale
that leaves a linear scar. The rhizomes are unbranched and may be distinctly
yellowish. Several exotic species naturalized in Florida, though larger and
more conspicuous than the native species, have large vertically oriented tubers
rather than horizontal rhizomes.
References:
Al-Shehbaz IA, Schubert BG. The Dioscoreaceae in the
southeastern United States. J. Arnold Arbor. 1989;70:57–95.
Bartlett HH. The source of the drug Dioscorea, with
a consideration of the Dioscoreae found in the United States. U.S.D.A. Bur
Pl Industry Bull. 1910;189:1–29.
British Herbal Medicine
Association. British Herbal Pharmacopoeia. BHMA; 1996:187.
Raz L. Dioscoreaceae. In: Flora of North America
Editorial Committee, eds. Flora of North America, vol. 26. New York, NY:
Oxford University Press; 2002:479–485.
Youngken HW. Text-Book of Pharmacognosy, 5th ed. Philadelphia, PA: The
Blakiston Company; 1943:200–204.
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