pronounced: dy-oh-SCOR-ee-uh uh-LAR-tuh
Dioscorea was named for Pedanius Dioscorides (c.40 AD — c.90 AD), Greek physician and pharmacologist, whose work De materia medica† was the foremost classical source of modern botanical terminology and the leading pharmacological text for 16 centuries. Alata is from the Latin ala, a wing.
The species is native to south-east Asia, and probably to surrounding areas such as Taiwan, some of the Japanese islands, Assam, the lowland areas of Nepal, New Guinea and Christmas Island. It has escaped from its native growth area into the wild, and has become naturalized in many other parts of the world, including Australia, where it grows in the northern parts of the country, and is now extending into northern NSW.
This is a vigorous twining herbaceous vine, twining clockwise, an important edible tuber crop, but also an invasive plant outside cultivated areas, when it can displace native species. Its root system is fibrous, shallow (to about 1 m deep). The tubers are usually single, varying in size and shape, usually cylindrical, clavate or globose, often variously lobed or fingered. The tuber skin is brown to black; the flesh may be white, cream or purplish.
The stems are quadrangular, with 4 longitudinal winged, undulate green or reddish projections. The bases of mature stems are cylindrical and spiny. The leaves are mostly opposite, although they may be alternate on branches of rapid growth. They are coriaceous, broadly ovate, 10 - 30 cm by 5 - 18 cm, the apex acute or acuminate, or sometimes reflexed, the base cordiform. The upper surface of the leaf is dark green and shiny, with sunken venation; the lower surface is a paler green, and the veins are prominent. The petioles are 4 - 12 cm long, 4-winged, forming an auricular sheath at the base, with a pair of pseudostipules that clasp the stem.
Wrinkled bulbils are produced, often elongate and up to 15 cm in length.
The species is dioecious. The staminate inflorescences are axillary, 1 or 2 per axil, paniculate, fasciculate. The panicles bear flowers singly, bracteolate, in a zigzag pattern along the rachis, which can be up to 25 cm long. The secondary 1 - 3 axes (sometimes more) are fasciculate, less than 3 cm, each subtended by a deltate-ovate bracteole shorter than 1 mm. The pistillate inflorescences are solitary, 4 - 20-flowered, 6 - 35 cm long. The staminate flowers have a whitish cup-shaped perianth; the tepals are about 1 mm, connate at the base in 2 subequal whorls, the outer widely ovate, the inner narrower, the apex obtuse to rounded in both. There are 6 fertile stamens in 2 equal whorls, with the anthers longer than the filaments. In the pistillate flowers, the perianth is lightly coloured, the tepals broadly ovate. There are 6 staminodes, smaller than the fertile stamens. Staminate flowers may remain open for 4 - 5 hours, while pistillate flowers open for 9 - 11 days.
The fruit is a 3-locular capsule, 2 - 3 cm wide, each locule flattened like a wing, with 2 seeds inside. The seeds are orbicular, winged all round, and are frequently unviable.
The total growing period is 8- 10 months, after which the plant dies back, and the tubers enter a dormant period of 2 - 4 months before sprouting again.
This is the most extensively cultivated of all the edible yams. There are hundreds of cultivars, varying in the colour and consistency of the flesh. The bulbils may also be eaten. Typically the plants are propagated vegetatively.
Where the plant has escaped into the wild, it spreads rapidly into natural forests, climbing into the canopy of mature trees and forming dense stands.
