Common Name Chinese yam
Note: Edible species of Dioscorea have opposite leaves whilst poisonous species have alternate leaves.
Dioscorea opposita is an exception to the rule that yams must be cooked before consumption (due to harmful substances in the raw state). In Japanese cuisine, it is eaten raw and grated, after only a relatively minimal preparation: the whole tubers are briefly soaked in a vinegar-water solution, to neutralize irritant oxalate crystals found in their skin. The raw vegetable is starchy and bland, mucilaginous when grated, and may be eaten plain as a side dish, or added to noodles.
The tuber has a floury texture with a very pleasant flavour that is rather like a potato. The tubers can be boiled, baked, fried, mashed, grated and added to soups. They store well and for a long time and can also be left in the ground and harvested as required in the winter, providing ground does not freeze. This is a top quality root crop, very suitable for use as a staple food. An arrowroot can be extracted from the root, though this is not as good at binding other foods as the starch from D. japonica. The root contains about 20% starch. 75% water, 0.1% vitamin B1, 10 - 15 mg% vitamin C.
The Chinese yam, called "Shan Yao" (山药- literally mountain medicine) in Chinese herbalism, is a sweet soothing herb that stimulates the stomach and spleen and has a tonic effect on the lungs and kidneys. The tuber contains allantoin, a cell-proliferant that speeds the healing process. The root is an ingredient of "The herb of eight ingredients", traditionally prescribed in Chinese herbalism to treat hyperthyroidism, nephritis and diabetes. The tuber is anthelmintic, digestive and gently tonic. It is used internally in the treatment of tiredness, weight loss, poor appetite, poor digestion, chronic diarrhoea, asthma, dry coughs, frequent or uncontrollable urination, diabetes and emotional instability. It is applied externally to ulcers, boils and abscesses.