. Yam plants PLANT DESCRIPTION: Yams are a very ancient food plant, believed to have been cultivated for more than 12,000 years. They are twining vines with shiny, heart-shaped, purple-tinged leaves and grow from underground tubers which have a brown skin and white flesh and can weigh many kilos. Yams require a fertile, well-drained soil with a high organic matter content. Plant at the beginning of summer in areas that receive a wet season. They will grow in full sun or semi-shade but need a trellis. Plants need plenty of water during the growing season. Dioscoreaceae, consisting of more than 800 species of climbing vines and woody shrubs. Many members of the yam family produce subterranean tubers or tuberous stems, and have heart-shaped leaves, small green or white flowers, and a ...