Glutinous Yam, Japanese yam
Dioscorea japonica
Family: Dioscoreaceae
What it is like
Dioscorea japonica is a PERENNIAL CLIMBER growing to 3 m (9ft 10in). See above for USDA hardiness. It is hardy to UK zone 8. It is in flower from September to October. The species is dioecious (individual flowers are either male or female, but only one sex is to be found on any one plant so both male and female plants must be grown if seed is required). . The plant is not self-fertile. Suitable for: light (sandy), medium (loamy) and heavy (clay) soils and prefers well-drained soil. Suitable pH: mildly acid, neutral and basic (mildly alkaline) soils. It cannot grow in the shade. It prefers moist soil.
Height (m): 3
Where it is found
Wooded foothills. Mixed forests and margins, scrub forests, herb communities, mountain slopes, valleys, along rivers and streams, roadsides; 100 - 1200 metres.
E. Asia - China, C. and S. Japan.
Conservation Status:
Countries/locations it is found in
How it is used
Food
Rating: 4
Tuber - cooked. A very pleasant mild flavour with a floury texture, the roots can be eaten as a potato substitute. The starch can be used as a binding agent for other foods. Roots contain about 1.9% protein, 20% carbohydrate, 0.1% fat and 1% ash. Leaf tips - cooked. Tubercles - cooked.
Root: includes bulbs, corms, tubers, rhizomes etc.
Medicine
Rating: 2
The tubers are prescribed in the treatment of diarrhoea, enteritis, enuresis and spermatorrhoea. They are also dried and cut into shavings then used as a tonic. The roots of most, if not all, members of this genus, contains diosgenin. This is widely used in modern medicine in order to manufacture progesterone and other steroid drugs. These are used as contraceptives and in the treatment of various disorders of the genitary organs as well as in a host of other diseases such as asthma and arthritis.
Contraceptive: Prevents fertilization occurring in females.
Miscellany: Various medicinal actions that need more clarification.
Tonic: Improves general health. Slower acting than a stimulant, it brings steady improvement.
Other
Rating: 0
Miscellany: A rag-bag of items that are difficult to categorise.
Food Forest: Plants for Edible Forest Gardens and Food Forests.
How it is grown
We have very little information on this species and do not know if it will be hardy in Britain, though judging by its native range it could succeed outdoors at least in the mildest areas of this country. The following notes are based on the general needs of the genus. Easily grown in a fertile well-drained soil in a sunny position or light shade. Prefers a rich light soil. Plants produce tubercles (small tubers that are formed in the leaf axils of the stems), and can be propagated by this means. A climbing plant that supports itself by twining around the branches of other plants. Dioecious. Male and female plants must be grown if seed is required. For polyculture design as well as the above-ground architecture (form - tree, shrub etc. and size shown above) information on the habit and root pattern is also useful and given here if available. Growth habit is a single or multiple shooting vine from a crown. Herbaceous. The root pattern is tuberous with swollen potato-like roots .
Propagating it: Seed - sow March to April in a sunny position in a warm greenhouse and only just cover. It germinates in 1 - 3 weeks at 20°c. Prick out the seedlings as soon as they are large enough to handle and grow on in a greenhouse for their first year. Plant out in late spring as the plant comes into new growth. Basal stem cuttings in the summer. Division in the dormant season, never when in growth. The plant will often produce a number of shoots, the top 5 - 10 cm of the root below each shoot can be potted up to form a new plant whilst the lower part of the root can be eaten. Tubercles (baby tubers) are formed in the leaf axils. These are harvested in late summer and early autumn when about the size of a pea and coming away easily from the plant. They should be potted up immediately in individual pots in a greenhouse or cold frame. Plant out in early summer when in active growth.
Best place to grow: Woodland Garden Sunny Edge; Cultivated Beds;
Habit: Perennial Climber
Hardiness: 7-12
Growth:
Soil: Light (sandy), medium, heavy (clay)
Shade: No shade
Moisture: Moist
Things to keep in mind
Edible species of Dioscorea have opposite leaves whilst poisonous species have alternate leaves.
Its other names
Local names
Yamaimo, Japanese Wild Yam, Glutinous Yam, Japanese Cinnamon Vine, mukago, East Asian mountain yam, Japanese mountain yam, French: igname du Japon