Dioscorea polystachya aka Chinese Yam

Dioscorea polystachya is called Chinese yam or cinnamon vine. It belongs to the yam family, Dioscoreaceae. Its native range spans the southern Russian Far East, China, the Kuril Islands and Taiwan. It grows in temperate regions and loses its leaves seasonally. The older name Dioscorea batatas refers to this same species. People grow it for food and use it in Chinese medicine.

This fast-growing perennial vine climbs by twining around supports. Its stems reach 11 feet (3.4 metres) or more. The green or purple stems can have angles and a powdery coating. Long leaf stalks bear glossy, green, heart-shaped leaves with three lobes. Leaves may grow in pairs, alternate along stems, or form whorls. Round, warty bulbils form where leaves join the stems. These small tubers can grow into new plants. The long underground tuber reaches 2–3 feet (0.6–0.9 metres).

Small white flowers appear from mid- to late summer. They grow in clusters where leaves meet the stems. Their scent recalls cinnamon, though the plant does not always flower. Small capsules split to release winged seeds. Both seeds and tubers help the plant spread. Its leafy growth can form thick cover over other plants. This makes its spread a greater concern than its flowers.

Chinese yam grows in full sun or light shade. It prefers fertile soil that drains well and stays moist. NC State lists it for USDA zones 5–9. Plants for a Future reports hardiness to at least −18°C. Plants take three to four years to reach full maturity. Its value as a food crop comes from its starchy tubers. Cooks can boil, bake, fry or mash them. Cooking is the safer choice, despite reports of raw use. Uncooked tubers can irritate skin and burn the mouth or throat. Calcium oxalate crystals cause these effects.

In parts of the United States, this vine has become invasive. It has spread from Louisiana north to Vermont. Dense growth can smother native plants and even kill trees. It colonises moist, disturbed sites and needs substantial control. NC State advises choosing native vines instead for landscapes. It reports no major pest problems locally. Possible problems include fungal and viral diseases, scale, nematodes and mealybugs. Its food uses do not remove its risks to people or habitats.