Dioscorea japonica aka Japanese Yam

Dioscorea japonica is a vine that lives for many years. It belongs to the yam family, Dioscoreaceae. Its names include Japanese yam, glutinous yam, and yamaimo. Its native range runs from Assam to Japan. Records place it in China, Korea, and Taiwan. They also place it on several islands in Japan. Kew puts it in the subtropical climate zone. It is not native to Britain or Ireland.

This vine grows from tubers, reaching about 10 feet (3 metres) tall. Its stems wind around nearby plants' branches for support. Small tubers, called tubercles, grow where leaves meet the stems. These can grow into new plants. In the wild, it grows in woods and along forest edges. It also grows in scrub, valleys, and on mountain slopes. Other sites include stream banks, roadsides, and wooded foothills. Records span heights of about 330–3,940 feet (100–1,200 metres).

Plants For A Future gives September to October as its bloom time. Each plant bears either male or female flowers. Plants of both sexes must grow together to make seeds. A lone plant cannot use its own pollen to set seed. In gardens, it suits sunny woodland edges and planted beds. Plants For A Future also lists it for food forests. Its stems need nearby plants or some other support to climb.

The species profile calls for moist soil that drains well. It accepts sand, loam, and clay soils. It also grows in soils from mildly acid to mildly alkaline. The profile says it cannot grow in shade. Plants For A Future gives USDA zones 7–12. Yet its notes leave doubt about withstanding British cold. They suggest that only Britain's mildest sites may suit it. Keep that caution in mind when using the zone range.

You can eat the tubers that grow below ground once cooked. They taste mild and have a floury feel. They can take the place of potatoes in meals. Their starch can help bind other foods. The source also lists cooked leaf tips and stem tubercles as edible. It records past uses of the tubers as medicine. People have used them for diarrhoea and some urinary complaints. They have also used dried tuber shavings as a tonic. These records do not prove that those treatments work. The supplied evidence gives no pest or disease account for this species. Nor does it show that the plant is safe for pets.