Chinese Yam

About 600 species make up this large genus of tuberous, deciduous or evergreen, twining climbers, which are widely distributed in the tropics and subtropics. A few are grown as ornamentals and many are cultivated as food crops in warm regions. Some of the edible yams produce very large tubers —those of Dioscorea alata (white yam) can reach 50kg (110lb). The common name "yam" is from a W African dialect word meaning "eat". Many species contain steroidal saponins, used in the preparations of steroids by the pharmaceutical industry. The discovery of hormones in yams was made in 1943 by Russel E. Marker, an eccentric American organic chemist who produced progesterone from Mexican yams in a pottery shop-cum-laboratory, and presented two jars of the hormone, then worth $160,000, to the pharmaceutical firm Laboratorios Hormona (later to become Syntex), thus initiating production of an affordable contraceptive pill. Until the hormone diogenin was synthesized in 1970. D. macrostchya (Mexican yam) was the sole source for manufacture of contraceptive pills. A small Himalayan species, D deltoidea, has proved the richest of all yams in steroidal saponins; it is now endangered from over-collection. Dioscorea batatas, the hardiest of the commercially cultivated yams, contains allantoin, a cell proliferant also found in Symphytum officinale (See, comfrey). Various yams are used in traditional medicine. D. batatas, D. hypoglauca, and D. nipponica are used in Chinese medicine for rheumatic, digestive, or urinary complaints. The N American D. quaternata has similar uses to D. villosa. Known as aluka, yams are also used in Ayurvedic medicine for sexual and hormonal problems and hysteria.

Perennial climber with vertical tubers, to 1m (3ft) long, and heart-shaped, pointed leaves, 4-8cm (1½-3in) long. Bulbils form in leaf axils. Tiny white, cinnamon-scented flowers are produced in axillary spikes (male and female separate), followed by 3-angled capsules.rm

Common Name:	Chinese Yam
Other Names:	Cinnamon yam
Botanical Name:	Dioscorea batatas syn. D. opposita
Genus:	Dioscorea
Family:	Dioscoreaceae
Native Location:	China, Japan, Korea, Taiwan
Cultivation:	Rich, well-drained soil in sun or partial shade. Tubers may rot in cool, damp conditions when dormant.
Propagation:	By seed sown in spring at 19-24°C (66-75°F); by division or sections of tubers in autumn or early spring; by bulbils planted in spring.
Harvest:	Tubers, roots, and rhizomes are lifted in autumn. Dioscorea batatas is used raw or baked with flour or soil, according to diagnosis, and D. villosa is dried for use in liquid extracts or used fresh for homeopathic preparations.
Height:	3m (10ft)
Hardiness:	Z5
Parts Used:	Tubers (shan yao)
Properties:	A sweet, soothing herb that stimulates the stomach and spleen and has a tonic effect on the lungs and kidneys.
Medicinal Uses:	Internally for poor appetite, chronic diarrhea, asthma, dry coughs, frequent or uncontrollable urination, excessive thirst, or sweating, diabetes, and emotional instability associated with qi deficiency. An ingredient of "The Pill of Eight Ingredients", a traditional Chinese remedy for diabetes, kidney problems, and under-active thyroid. Externally for boils and abscesses.
Culinary Uses:	Tubers yield starch, known as Guiana arrowroot, and are eaten boiled, baked, mashed, or fried. Often combined in tonic soups with Lycium barbarum (See, Duke of Argyll's tea tree) and Polygonatum odoratum (See, angled Solomon's seal).
Bibliography:	Encyclopedia of Herbs by Deni Brown Copyright © 1995, 2001 Dorling Kindersley Limited. Pg 194