keys to the vascular plants of east texas - Botanical Research ...

656 DIOSCOREACEAE/DIOSCOREA
sapogenin diosgenin) used by the pharmaceutical industry for anti-inflammatory medications
(e.g., cortisone) and the active ingredients in early birth control pills (Martin 1969; Lewis &
Elvin-Lewis 1977; Huber 1998; Judd et al. 1999). (Named for Dioscorides, Greek naturalist of the
first century A.D., who wrote De Materia Medica, a description of ca. 600 plants used medicinally,
and “who served as a physician in the army of the Roman emperors Claudius and
Nero”—Bouman 1995)
REFERENCES: Bartlett 1910; Xifreda 2000.
1. Plants with conspicuous, axillary, aerial bulbils; leaves usually all alternate; petioles with flanged
or auriculate (= with earlobe-like appendages or flaps of tissue) bases; rhizomes absent, tubers
present or not so; introduced species ________________________________________________ D. bulbifera
1. Plants without aerial bulbils; leaves of at least lower nodes usually opposite or in whorls;
petioles without auriculate bases; rhizomes present; native species ___________________________ D. villosa
Dioscorea bulbifera L., (bulb-bearing), AIR-POTATO, AIR YAM, AERIAL YAM, POTATO YAM. Underground
tubers small or absent; stems to 6(–20) m or more long, twining counter-clockwise (this
is also referred to as sinistrorse = twining upward from right to left), with conspicuous, axillary,
subspherical or angled, aerial bulbils, these sometimes huge (up to 2 kg)—Huber (1998) indicated
that these structures would better be referred to as tubers; leaves usually all alternate; leaf
blades 5–25 cm long, to 18(–26) cm wide; petioles auriculate or flanged at base; capsules to ca.
2.5 cm long. Deep woods, along stream banks; Cass Co. (Amerson 274, BRIT; label noted that “tubers
produced on aerial stems”; Correll 1972a) in the Pineywoods; FL, LA, MS, and TX. Late summer–early
fall; however, plants growing in North America rarely flower, and those that do are
typically pistillate (Raz 2002). Native of tropical Asia and possibly also Africa. This species
contains diosgenin, alkaloids, oxalates, and other toxins (Morton 1982); it has both inedible and
edible forms (Bailey & Bailey 1976). It is cultivated (primarily in Oceania) for the aerial bulbils
and was introduced to the New World during the slave trade (Al-Shehbaz & Schubert 1989).
This species can be distinguished from another introduced bulbil-bearing species, D.
polystachya Turcz. (incorrectly referred to by some authors as D. oppositifolia), CHINESE YAM,
CINNAMON VINE (known from AR and much of the e U.S.); the latter has nonauriculate petiolar
bases, usually opposite leaves, and dextrorse (= twining upward from left to right—clockwise)
stems (Al-Shehbaz & Schubert 1989; Ting & Gilbert 2000; Raz 2002). � I m/285
Dioscorea villosa L., (soft-hairy), WILD YAM, ATLANTIC YAM, COLIC ROOT, YAM ROOT, FOUR-LEAF
YAM. Rhizomes 5–15 mm thick, � smooth and straight, from not much branched to contorted
irregularly or with many short branches; stems to 5 m long, sinistrorse; leaves, except for the
lowest, all alternate or those of lower nodes whorled and those above opposite to alternate; leaf
blades 5–15 cm long; capsules 1.2–3 cm long; seeds 7–18 mm wide. Low to moist rich woods;
mainly Pineywoods, also Anderson (Fleming et al. 2002) and Madison (Turner et al. 2003) cos.
near the e margin of the Post Oak Savannah and in Red River drainage w to Lamar (BRIT); se
Canada (Ont.) and e U.S. from NY s to FL w to MN and TX. Apr–Jun. [D. quaternata J.F. Gmel., D.
villosa var. glabrifolia (Bartlett) Fernald] Native TX Dioscorea have traditionally been divided into
two species, D. quaternata and D. villosa (e.g., Correll & Johnston 1970; Turner et al. 2003). However,
we are following Raz (2002) who synonymized D. quaternata with D. villosa, indicating, “At
present, I can find no natural gaps in the variation between the plants that have been called (albeit
ambiguously; see H.H. Bartlett 1910) D. villosa and those called D. quaternata.” Raz (pers. comm.)
further indicated that while there are morphological extremes that can be recognized, “every
morphological intermediate that can exist between these extremes, does in fact exist.” While the
indigenous species have low levels of saponins, the rhizomes of D. villosa were used by some Native
Americans to ease the pain of childbirth, and an alcohol extract was used in the 19th century as a
treatment for colic (Raz 2002). If one chooses to recognize two native species in TX, characters
such as the following might prove useful in recognizing the “morphological extremes”: