Dioscorea alata aka Greater Yam

Dioscorea alata is a perennial vine in the yam family. It lives for more than one year. Its names include water yam, white yam, and winged yam. Kew places its native range in tropical Asia. Useful Tropical Plants suggests people first grew it in Asia. That source reports no known wild habitat for the plant. People spread it across oceans long ago as a food crop. Growers now raise it in many tropical and subtropical regions.

The vine grows fast from a large underground tuber. Its new stems climb supports or trail over the ground. Garden plants can reach about 30 feet [9.14 metres] tall. Their spread can reach 6 feet [1.83 metres]. Other accounts give stem lengths of 49 feet [15 metres]. The stems have four sides and purple wing-like edges. They twine to the right around nearby supports. The broad, egg-shaped leaves are bright green. They grow on long stalks. Each leaf has five to seven deeply marked veins. Leaves can reach about eight inches long.

Yellow-white flowers appear by season, not in a fixed month. Plants For A Future says plants seldom form seeds when grown. The vine also makes small tubers above ground, called bulbils. Growers can raise new plants from these or cut tubers. Tubers below ground yield a large crop of starchy food. Plants For A Future reports about three tubers per plant. Each often weighs five to ten kilograms.

Give this vine sun or partial shade and a firm support. It grows best in deep, rich soil that drains well. Sandy loam helps tubers grow, but waterlogged soil does not. Keep the soil moist and avoid letting it dry out. Missouri Botanical Garden lists USDA hardiness zones 9–11. Useful Tropical Plants says the plant cannot cope with frost. In tropical regions, it rests after the rainy season. This dormant phase may last two to three months. Gardeners grow it for food, leaves, and climbing cover. It can grow on trellises, porches, pergolas, or in pots.

Seeds, tubers, and bulbils can spread the plant beyond its bounds. It can become invasive. Gathering tubers and taking off bulbils can help curb its spread. Serious pest and disease trouble is not usual. Anthracnose and diseases caused by viruses can still harm the vine. Aphids, scale insects, and mealybugs may attack its growth. Nematodes can harm the tubers below ground. Cook both underground tubers and bulbils well before eating them. Raw tubers contain saponins and can cause toxic effects. People eat cooked tubers as vegetables or make flour and starch. Folk medicine uses the plant. But clinical evidence does not support claims that it treats illness.