Common Name: Water Yam

General Information

Dioscorea alata is a vigorous, perennial, climbing plant, producing annual stems up to 15 metres long from a very large tuberous rootstock[]. These stems scramble over the ground, or twine into the surrounding vegetation[]. The stem is quadrangular, winged, and twines right-handed[].
The plant is widely cultivated in tropical areas for its edible root[]. A very polymorphic species, originating in SE Asia and not found wild, it was dispersed by humans over the Pacific and Indian Oceans in prehistory, and is now widespread in the Region and pantropics[]. The plant has a dormancy period of at least two months, making it easier to transport and probably accounting for why it became so widespread[].

Known Hazards

Edible species of Dioscorea have opposite leaves whilst poisonous species have alternate leaves[].
The uncooked tuber of this species is toxic, and is said to produce narcosis[]. Saponin is present and cooking renders the tubers safe to eat[].

Botanical References

Range

Probably arose in cultivation in E. Asia - Malaysia.

Habitat

Not known in a wild state.

Properties

Edibility Rating
Medicinal Rating
Habit	Perennial Climber
Height	15.00 m
Self-fertile	No
Cultivation Status	Cultivated, Wild

Cultivation Details

Plants grow best in lowland tropical areas up to an elevation of 1,000 metres with a temperature around 26 - 34°c; a well-defined dry season of 4 - 5 months; and a total rainfall of 1,000 - 1,500mm evenly distributed throughout the remainder of the year[]. Plants are not frost tolerant[]. Amongst the many cultivars of this species, there are forms that are tolerant of a wide range of environmental conditions[].
For best yields, this species requires a deep, well-drained, sandy loam that is not liable to water-logging[]. It also grows well in medium to clay loams[]. Although more tolerant of poor soils than most other members of this genus, plants respond well to the application of organic matter[]. Prefers a pH in the range 5.5 - 6.5, tolerating 4.8 - 8.5[].
Daylengths of more than 12 hours are preferred during the early growing season since this encourages vegetative growth; daylengths of less than 12 hours towards the end of the growing season will encourage tuber formation and development[].
Plants take 7 - 10 months to mature a crop[]. Yields of 20 - 25 tonnes per hectare have been obtained[].
There are some named varieties[, ].
A dioecious species, both male and female plants need to be grown if seed is required.

Edible Uses

Root - cooked[]. Usually boiled or baked and used as a vegetable[, ]. An average of 3 roots are produced by the plants, these usually each weigh in the range of 5 - 10kg, though exceptionally they can weigh up to 60 kg[]. The root needs to be properly cooked, it can be toxic if eaten raw[].
The plant produces small aerial tubers in the leaf axils, and these can be eaten in the same way as the tubers[, ].

Medicinal

The tuber is grated, mixed with brown stout vinegar, then spread onto paper and placed on the small of a woman's back to prevent or forestall a threatened miscarriage[].

Other Uses

None known

Propagation

Seed - rarely produced in cultivation, they are not normally used to propagate this species.
Cuttings of tubers. Small tubers can be cut into 2 - 4 sections, larger ones into 6 - 8 sections. Each section should have 2 - 3 dormant buds. The cut tuber is often left in the sun for several hours to promote wound healing and reduce the risk of fungal infection[].
Aerial tubers can also be used, they usually produce vigorous plants[].

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