Dioscorea wallichii (kruo)
A yam from Southeast Asia, India and China, Dioscorea wallichii has edible tubers that can grow to over one metre long.
About this species
Dioscorea wallichii was named by Joseph D. Hooker (1817-1911) in honour of Nathaniel Wallich (1786-1854), a surgeon and botanist who was involved in the development of the Botanic Garden, Calcutta. The tubers of D. wallichii are edible when boiled and peeled but are buried deep under the soil so they can be hard to extract.
Geography & Distribution
Dioscorea wallichii is found in India, Bangladesh, Burma, Thailand and China. It climbs on large shrubs or trees in mixed deciduous forest and evergreen montane forest. It also occurs in disturbed areas along roadsides and edges of cultivated areas.
Herbarium specimen of a female plant of Dioscorea wallichii with fruits
Overview: A large, hairless climber that can grow to at least 20 m long. It has one edible, cylindrical tuber (or sometimes one that is used for growth whilst new one is forming) that can be over 1 m long and 3–6 cm wide. The tuber is white when young, becoming yellow and stringy with age.
Stem and leaves: The right-twining stem is woody and armed with spines at the base, herbaceous above and round in cross-section. Leaves are usually 8–19 x 8–21 cm and are more or less heart-shaped, with 5–7 main veins.
Flowers: Like almost all yams (Dioscorea species), D. wallichii has separate male and female plants. The female inflorescences (flowering structures) hang down from the vine, each one containing up to 20 flowers. Male inflorescences are also pendent, and the male flowers are green and about 1 mm long.
Fruits: Round capsules contain flat, brown seeds, each with a thin, marginal wing.
Threats & Conservation
Common and widespread within its natural range, Dioscorea wallichii is not considered to be threatened. It appears to be tolerant of some disturbance, judging from the areas where it is found, hence the species is listed as Least Concern. As with all edible species, it is desirable to monitor sustainability of use on a local level.
Conservation assessments carried out at Kew
Herbarium specimen of Dioscorea wallichii (male plant)
Dioscorea wallichii is being monitored as part of the IUCN Sampled Red List Index for Plants project, which aims to produce conservation assessments for a representative sample of the world’s plant species. This information will then be used to monitor trends in extinction risk and help focus conservation efforts where they are needed most.
Tubers of Dioscorea wallichii are consumed on a local scale as a source of carbohydrates. They are eaten by ethnic groups such as the Sakai tribe, who live in the Banthad Range in Peninsular Thailand. They are also eaten by tribes in Orissa, India, during the winter months. In other areas of India, D. wallichii has been described more as a famine food used in times of food shortage because the tubers are hard to extract and less desirable than those of other Dioscorea species.
In India, juice extracted from the tubers is drunk to treat jaundice.
This species at Kew
Pressed and dried specimens of Dioscorea wallichii are held in Kew’s Herbarium, where they are available to researchers from around the world by appointment. The details of some of these specimens can be seen online in Kew’s Herbarium Catalogue.
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