Dioscorea crispata Roxb.
Dioscorea heterophylla Roxb.
Dioscorea latifolia Benth.
Dioscorea oppositifolia Campbell.
Dioscorea papilaris Blanco
Dioscorea pulchella Roxb.
Dioscorea sativa Thunb.
Dioscorea sylvestris De Wild.
Dioscorea tunga. Hamilton.
Dioscorea violacea Baudon
Common Name: Aerial Yam
Aerial yam is a glabrous-leafed, non-spiny, perennial climbing plant producing annual stems up to 10 metres long from a woody, tuberous rootstock[
]. These stems scramble over the ground, or twine into the surrounding vegetation[
]. The stems twine left-handed and produce aerial axillary bulbils[
The plant is often cultivated in tropical areas, mainly for its edible aerial bulbs, though also for its roots[
Edible species of Dioscorea have opposite leaves whilst poisonous species have alternate leaves[
The aerial bulbs of this species contain toxic substances, including the alkaloid dioscorine[
]. This can be destroyed by thorough cooking[
]. Asiatic forms of the plant usually contain less alkaloids than plants originating in Africa[
]. There are forms that are almost or entirely free of toxins[
E. Asia - Malaysia.
|Cultivation Status||Cultivated, Wild
A plant of the moist, lowland tropics. It grows best in areas where annual daytime temperatures are within the range 20 - 30Â°c, but can tolerate 12 - 38Â°c[
]. It can be killed by temperatures of 9Â°c or lower[
]. It prefers a mean annual rainfall in the range 1,200 - 2,600mm, but tolerates 900 - 4,000mm[
]. It prefers a well-defined dry season of 2 - 3 months[
]. This species is more tolerant than most other yams of temperatures below 25Â°c[
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 6 - 6.7, tolerating 5.3 - 8[
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[
The bulbils are produced in 5 - 6 months from planting, though some forms can produce a crop in as little as 3 months[
]. Average yields of the bulbs are in the range of 3 - 5 tonnes per hectare, though up to 15 tonnes have been obtained[
The bulbils of selected cultivars tend to be angular with a flattened shape and a skin-colour which evokes the name 'turkey liver yam'. They may attain as much as 2 kg in weight but an average weight is about 0.5 kg. Races with increased bulbil production tend to show a reduction of the tuber, and in those with the highest bulbil return the tuber is but a woody rootstock[
]. Bulbils are ready for harvesting when they fall off the plant at a slight touch[
When produced, yields of 2 - 8 tonnes per hectare of the roots have been obtained[
There are some named varieties[
Aerial yam is a species of many races[
]. The wild ones, which are toxic raw, have globose, dark brown to liver-coloured, non-angular bulbils which serve as a famine-food, as do the tubers[
]. Wild strains are often planted intermixed with or on the perimeter of plantings of improved races as a protection against thieving[
]. Cattle eating them accidentally may be fatally poisoned showing frothing at the mouth and bloating[
The species is in the process of ennoblement and selected cultivars show in varying degree bitterness and poisonousness. Of some races even after prolonged preparation the bulbils remain bitter. Superior races are said to be very palatable and sweet, and to be entirely free from toxic substances so that consumption, even raw, is safe[
]. The skin is grey, lighter coloured than the wild forms, and the flesh is pale yellow to near white[
A dioecious species, both male and female plants need to be grown if seed is required.
Aerial tubers - cooked[
]. An agreeable taste, they can be boiled, baked, fried etc[
]. They must be thoroughly cooked in order to destroy toxic alkaloids[
]. Wild forms of the plant are always toxic raw, though selected cultivars have been developed that are much lower, or even free from, the toxins[
]. The tubers are produced, and can be harvested, over a long period of time[
Root - cooked[
]. Roots are usually around 0.5kg, though they can be up to 1.5kg[
]. They are not always produced by the plants[
The inflorescences are apparently eaten[
The juice of the roots is taken to expel threadworm[
]. The juice is dripped into wounds to expel worms and germs[
Both the tuber and the bulbil of wild races have medicinal uses[
In particular they are used externally, usually as a poultice, to treat wounds, sores, boils and inflammations; in dressings for treating dermal parasitic and fungal infections; or crushed, mixed with palm oil, and massaged onto areas of rheumatism, and for troubles of the breasts and for jiggers[
In India the tuber is considered to be diuretic and to be a remedy for diarrhoea and haemorrhoids[
The fruits are used to treat boils and for fever[
Sap expressed from the vine stems is applied to treat purulent ophthalmia, and for snake-bite[
The leaves are used, often by steam-distillation, against pink-eye[
Various medically active substances have been detected in the plant.
Dioscorine has been detected in the tuber, though certain Nigerian material has been reported free of the alkaloid[
Alkaloids have been reported from the leaves and stems and particularly in the fruits[
Diosgenin has been detected at 0Â·45% concentration[
Saponin is present and a number of other pharmacologically active substances[
Seed - rarely produced, 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[
]. The aerial bulbs are often divided into 2 or more equal sized pieces[
]. Plants often need to be grown for two seasons in order to produce full-size aerial bulbs[