Closely related to the Asiatic species Dioscorea hispida[].

Common Name: Bitter Yam

General Information

Dioscorea dumetorum is a perennial climbing plant producing spiny stems up to 10 metres long from a shallow-seated, tuberous rootstock[]. These stems scramble over the ground, or twine into the surrounding vegetation[].
Sometimes cultivated in tropical areas of Africa for its edible root[]. It is an easily grown plant and also a heavy cropper[]. The plant is often purposely grown at spare points on the land as an insurance against famine years, and is also encouraged in hedgerows around a farm and especially on the edges of yam fields as a deterrent to human and animal marauders[].

Known Hazards

Edible species of Dioscorea have opposite leaves whilst poisonous species have alternate leaves[].
The roots of this species contain toxic substances, including the alkaloid dihydrodioscorine[]. This can be destroyed by thorough cooking[]. Cultivated forms of the plant contain much less alkaloids than wild plants[].
The physiological effect of the poisonous tubers is to paralyse the respiratory system[].

Botanical References

Range

Tropical Africa - Senegal to W Cameroons, and extending across the Congo basin to Angola.

Habitat

Common throughout the savannah region[]. Edges of lowland rainforest, dry evergreen forest, evergreen bushland, and on termite mounds in Brachystegia woodland, persisting in plantations, in secondary thickets as well as grasslands, to 1,700 metres[]

Properties

Edibility Rating
Medicinal Rating
Habit	Perennial Climber
Height	7.00 m
Cultivation Status	Cultivated, Wild

Cultivation Details

A plant of the moist tropics, where it is found at elevations up to 1,500 metres. It grows best in areas where annual daytime temperatures are within the range 25 - 32°c, but can tolerate 15 - 40°c[]. It can be killed by temperatures of 9°c or lower[]. It prefers a mean annual rainfall in the range 1,000 - 1,700mm, but tolerates 700 - 4,200mm[]. It likes a well-defined dry season of 2 - 5 months[].
Prefers a sunny position, also succeeding in light shade[]. For best yields, this species requires a deep, well-drained, sandy loam that is not liable to water-logging[]. 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 8 - 10 months to mature a crop, yields are considered to be higher than most other cultivated African yams[].
There are some named varieties[, ].
Genetic variation there certainly is: the plant has undergone a degree of ennoblement by man's selection so that there is recognized a number of edible cultivars. In Nigeria there are yellow, white and pale yellow forms. In N Nigeria two races, one poisonous, one not, can be distinguished by hairiness, the poisonous one being the more tomentose. Cultivars are numerous in Dahomey[].
There appears to be some variation in toxicity perhaps due to edaphic, phenologic or other cryptic factors. Material from the Congo has been reported free of active principles[].
A dioecious species, both male and female plants need to be grown if seed is required.

Edible Uses

Root - cooked[]. Most commonly seen as a famine food for when all else fails[], it has a rather bitter flavour[]. The roots are collected, peeled, cut into small pieces and soaked overnight to remove toxic substances before being cooked[]. Alternatively, the tubers are peeled and soaked in water for several days. Then they are washed, sliced and dried in the sun. The dried slices are pounded into flour and used for uji or ugali[]. The meal is coarse and starchy, and in Gabon is said still to retain a bitter taste even after cooking[]. It is particularly rich in scorbutic acid, especially when prepared with tamarind pods[]. Roots can weigh several kilogrammes[].

If the more poisonous forms are to be eaten, then there must be a detoxification which is carried out by slicing and steeping the root for 3 - 5 days in running water[]. A test for completion of the cleansing process is said to be to see if shrimps or fish are feeding around the basket in which the cut-up roots are suspended[]. If running fresh water is not available, salt water can be used[]. The roots can also be cleaned by burying them for three days in black cotton soil, or steeping in cotton soil and water, or with tamarind pods (Tamarindus indica) or desert dates (Balanites aegyptiaca)[].

Medicinal

The tuber is boiled and eaten, or the liquid can be drunk, in the treatment of jaundice and malaria[].
The root is considered a cure for schistosomiasis[].
The powder obtained from dried and pounded roots is soaked in water and used to treat bilharzia[].
The root is used topically as an anodyne to relieve pain[]. In Sudan it is used on rheumatic arthritis[]

Other Uses

None known

Propagation

Seed - 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[].

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