Dioscorea esculenta (Lour.) Burkill

Tubers as described above, protected by thorny roots in the wild plant and by man's vigilance in cultivation; skin of the tubers bright brown or gray-brown, thin so that the tuber is easily bruised, often rough with indurated bases of rootlets; flesh white, sometimes with a trace of bitterness at the surface, but on the whole sweet and esculent. When the tubers are many, they tend to be shortly cylindric with both ends rounded; when they are few and relatively larger as in various cultivated races, they may be lobed; sometimes they are large and may weigh over 3 kg. Plant pubescent with T-shaped hairs, the shank of which varies in length and when short brings the tomentum close down on the epidermis; the cross piece is of a single cell; exposed surfaces are glabrescent. Stems 1 or rarely more, terete, prickly at the base and diminishly so upwards: basal internodes carry prickles, medial at the nodes only, one at each side of the petiole and distal none. Leaves when very large to 15 by 17 cm, but most of them do not exceed 10 by 10 cm, acuminately acute at the apex, the forerunner tip a small mucro, 9-13-nerved; secondary nerves fairly regular but not conspicuously ladder-like; petiole 1-1½ times as long as the blade, sometimes with small prickles in its pubescence. Male flowering axes almost invariably solitary, carrying flowers one at a time or very rarely 2-4 in a small cyme, the flowers to 70 or more; axis slightly angled. Bracts ovate-acuminate, to 2½ mm long. Pedicels to 1¼ mm, but usually nearly absent. Torus a shallow cup. Outer tepals broadly lanceolate, acute, 1¾ mm, inner ones a trifle shorter. Stamens all alike inserted just below the perianth lobes, the vascular bundle strengthening the cup, forming a ridge; filament 1 mm long, curved so as to cause the anthers to dehisce upwards. Female flowering axes solitary from upper leaf axils, to 40 cm, de-curved, slightly angled. Bracts ovate, acuminate, 2 mm long. Pedicels in anthesis very short. Torus scarcely developed into a tube under the perianth lobes. Outer tepals lanceolate-ovate, obtuse, 1.5 mm long, inner ones more acute. Capsules (only one seen and it not quite ripe) reflexed, 27 by 12 mm, subretuse at the apex and nearly truncate at the base. Seeds winged all round.

A tropical plant. It grows from sea level up to about 1500 m but is mostly below 800 m. It cannot tolerate water-logging. It needs a reasonably long rainy season. It needs a loose fertile soil. It does poorly on sandy soils and becomes misshapen in heavy clay soils. High levels of organic matter promote growth. In the Philippines it occurs throughout Luzon and is also found in the Batanes Islands. It suits hardiness zones 9-12.

The tubers are cooked and eaten. They can be used in soups, stews, mashed or fried. The tubers are often cut into pieces, steeped in water, and boiled prior to eating. Young leaves are also recorded as being cooked with coconut milk and eaten.

Normally small tubers are planted (50-75 g) but cut portions of a tuber can be used. Using either the top section or the bottom section of a tuber gives better establishment and yield than middle portions. Using larger tubers gives larger individual tubers and higher yields for individual plants. Using a plant spacing of 30 cm between plants and 100 cm between rows about 2,000 kg of planting material are used if 70 g tubers are used. Tubers are planted 8-12 cm below the ground. It is possible to grow plants from stem cuttings where a leaf and node are propagated under mist. This method is normally only for increasing the amount of planting material of a selected variety. Planting in mounds makes harvesting easier. It also assists drainage and improves aeration. A spacing of 80-100 cm between plants is suitable. Planting is normally adjusted to fit in with the beginning of the rainy season. The growing season of 9-10 months is long and an extended wet season is therefore desirable. Stakes are required. Stakes 2 m long are sufficient. Lesser yams compete poorly with living plants used as shade. Weed control is probably most crucial during the first 3 months. As early growth of the plant is sustained from the tuber, fertilisers can be applied slightly after planting. Added nitrogen fertiliser is more effectively used when plants are staked. Nitrogen is of more benefit for leaf growth in the early stages of plant development. Potassium is beneficial but often phosphorus applications do not give significant responses as lesser yams are efficient at extracting it from the soil. High yields can be obtained.