Air Yam

Occasionally eaten. It is reported to contain a poisonous glycoside.

Dioscorea bulbifera is the most widely distributed of all Dioscorea species. It is found throughout the tropics and is thought to be native to both Africa and Asia. The tubers are either small and bitter or do not form at all. The bulbils are eaten, although this species is not widely consumed outside of Oceania. It is weedy in Florida and probably elsewhere in the Gulf States, but I have not seen any specimens to document its range outside Florida. Plants in the flora area rarely flower, and those that do are usually pistillate; I observed no staminate flowers.

Dioscorea bulbifera is used medicinally in China, but, unlike in Africa, it is not much used as a food plant.

Tubers mostly large, globose or pyriform. Stems glabrous, twining clockwise bearing numerous brown warted bulbils c. 2.5 cm in diameter. Leaves alternate, 4-5 cm long, 2.5-13.5 cm broad, ovate, more or less deeply cordate at the base, long acuminate, 9-nerved, petiole 2.5-12 cm long. Male spikes slender, drooping, 6.5-10 cm long, clustered in the axils or sometimes panicled; stamens 6, antheriferous. Female spikes simple, fascicled in the leaf axils, 10-25 cm long. Capsule c. 2 cm long, 1 cm broad, oblong. Seeds winged at the base.

Plants tuberous or not; tubers, when present, buried just below ground surface, not stalked, globose, weighing less than 1 kg. Stems twining counter-clockwise, climbing to more than 20 m, often flecked with purple, unwinged or rarely narrowly winged, terete, producing axillary bulbils frequently greater than 5 cm in diam. in leaf axils. Leaves alternate throughout, 5–25 × 5–26 cm; petiole usually somewhat shorter than blade, base clasping, basal lobes stipulelike, 1–4 mm wide; blade 5–11-veined, broadly ovate-cordate, glabrous, base orbicular, margins entire, apex long-acuminate. Staminate inflorescences axillary, borne singly, spicate or paniculate, cymose, to 70 cm; cymes reduced to 1 sessile bracteolate flower, internodes ca. 2 mm; secondary axes to 6 per node, fasciculate, subtended by deltate bracteoles or sometimes leafy bracts, 3–20 cm. Pistillate inflorescences borne singly or fasciculate, to 6 per axil, spicate; spikes bearing to 50 flowers, 6–40 cm, subopposite to 8 mm apart. Staminate flowers fragrant; perianth white, becoming purple; tepals in 2 similar whorls, spreading at anthesis, lanceolate, (1–) 2–5 mm; fertile stamens 6 in 2 equal whorls; anthers as long as or longer than filaments; thecae distinct, not spreading. Pistillate flowers: perianth greenish white, not changing color; tepals as in staminate flowers; staminodes 6, smaller than fertile stamens. Capsules not reflexed at maturity, longer than wide, 1.8–2.8 × 1–1.5 cm. Seeds unilaterally winged, 12–20 mm. 2n = 80, 100.

Tubers usually solitary, renewed annually, ovoid or pear-shaped, 4--10 cm thick; cork black; roots fibrous. Stem twining to left, glabrous, smooth. Bulblets purplish brown with orbicular spots, globose or ovoid, variable in size, weight to 300 g. Leaves alternate, simple; petiole 2.5--5.5 cm; leaf blade broadly cordate, 8--15(--26) × 2--14(--26) cm, glabrous, margin entire or slightly undulate, apex caudate-acuminate. Male spikes usually clustered in leaf axils or along leafless, axillary shoots, drooping, sometimes branched. Male flowers: solitary, ± contiguous along rachis; bract and bracteole ovate; perianth purple, lobes lanceolate; stamens 6, inserted at base of perianth, filaments nearly as long as anthers. Female spikes often 2 or more together, similar to male ones, 20--30 cm. Female flowers: staminodes 6, ca. 1/4 as long as perianth lobes. Capsule reflexed or drooping, straw-colored, densely purplish dotted, oblong-globose, 1.5--3 cm, glabrous, base and apex rounded; wings 0.25--0.7 cm wide. Seeds inserted near apex of capsule, dark brown; wing pointing toward capsule base, oblong, 1.2--1.6 × ca. 0.5 cm. Fl. Jul--Oct, fr. Aug--Nov.

Tropics of the Old World.

Distribution: A plant of the foothills ascending to about 1000-2000 m in the tropical and sub-tropical parts of Asia & Africa.

introduced; Fla.; tropical Asia; tropical Africa.

S Anhui, Fujian, S Gansu, Guangdong, Guangxi, Guizhou, Hainan, S Henan, Hubei, Hunan, S Jiangsu, Jiangxi, S Shaanxi, Sichuan, Taiwan, Xizang, Yunnan, Zhejiang [Bhutan, Cambodia, India, Japan, Korea, Myanmar, Thailand, Vietnam; Africa, Oceania].

150-2100 m

Fl. Per.: July-September.

Flowering late summer--early fall.

Near ponds, marshes, drainage canals, disturbed woods and thickets, waste areas; 0m.

Mixed forest margins, river banks, valley sides; near sea level to 2300 m.

Helmia bulbifera (Linnaeus) Kunth.