Water Yam, Purple yam, Greater yam, White yam

Dioscorea alata

Physical Characteristics

Dioscorea alata is an evergreen Perennial Climber growing to 15 m (49ft) by 0.5 m (1ft 8in) at a fast rate. See above for USDA hardiness. It is hardy to UK zone 10. The flowers are pollinated by Wind, Insects. The plant is not self-fertile. Suitable for: light (sandy), medium (loamy) and heavy (clay) soils, prefers well-drained soil and can grow in nutritionally poor soil. Suitable pH: mildly acid, neutral and basic (mildly alkaline) soils. It can grow in semi-shade (light woodland). It prefers moist soil.

Distribution

Probably arose in cultivation in E. Asia - Malaysia.

Habitats

Edible Uses

Edible Parts: Root Edible Uses: Colouring Root - cooked[ 300 ]. Usually boiled or baked and used as a vegetable[ 300 , 301 ]. 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[ 300 ]. The root needs to be properly cooked, it can be toxic if eaten raw[ 332 ]. The plant produces aerial tubers and these can be eaten in the same way as the tubers[ 301 ].

Medicinal Uses

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[ 348 ]. Although available as a dietary supplement and used in folk medicine, there is no clinical evidence that D. alata has any therapeutic properties. D. alata supplements may have adverse effects in people taking estrogens, anticoagulant drugs or during pregnancy and breast-feeding. D. alata has relatively high levels of oxalates (486–781 mg/100 g dry matter).

Known Hazards

Edible species of Dioscorea have opposite leaves whilst poisonous species have alternate leaves[ 174 ]. The uncooked tuber of this species is toxic, and is said to produce narcosis[ 332 ]. Saponin is present and cooking renders the tubers safe to eat[ 332 ].