Dioscorea batatas

Chinese Yam Dioscoreaceae

A wonderfully useful edible climber disguised as an ornamental, Dioscorea batatas is the name traditionally applied to the Chinese Yam, although Kew now treats it as a synonym of Dioscorea polystachya. Native from the Russian Far East and China through Korea, Taiwan and the Kuril Islands, it is one of the few edible yams genuinely suited to a temperate climate. 

A vigorous twiner, it produces attractive heart-shaped foliage and small, pleasantly cinnamon-scented flowers, while the real prize develops underground: long, cylindrical to spindle-shaped tubers which can exceed 1 m in length. They are an important traditional food crop in East Asia and may be boiled, baked, fried, mashed, grated or added to soups. Unusually among yams, the tuber can also be eaten raw, although cooking is the safer culinary approach. The aerial bulbils produced in the leaf axils are edible too. 

In China the tuber has a long history not only as food but in traditional Chinese medicine, where Chinese yam (shanyao) has been used for centuries. Traditional applications include preparations associated with digestion and general convalescence; modern research has investigated its polysaccharides, allantoin and other bioactive compounds, although these should not be confused with established medical treatments. 

For the garden, give it full sun or light shade and fertile, well-drained soil, with something substantial to climb through. It is remarkably hardy — reported to around −18°C — but harvesting the edible tuber is the tricky bit: it grows deeply and is extremely liable to break when dug. Perhaps best regarded as a perennial vegetable with a very long-term investment plan. 

Family: Dioscoreaceae
Distribution: Russian Far East to China, Korea, Taiwan and Kuril Islands
Edible: Underground tubers and aerial bulbils; cooked, or tuber raw
Ethnobotany: Important Chinese food and traditional medicinal plant
Flowering: July–September
Hardiness: H6, approximately −20 to −15°C
Height: 3–5 m
Spread: 1–2 m