DIOSCOREACEAE

The Dioscoreaceae or Yam family consists of 9–10 genera of monocotyledons of tropical or warm temperate regions, twining, leafy, sometimes woody vines, with rhizomes or tuberous roots. The most important genus is Dioscorea, several species of which are cultivated for their edible tubers. The inedible tubers of several Mexican species contain saponins and are gathered wild for the production of drug hormones.

Dioscorea villosa

Wild yam

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Family Dioscoreaceae

Description

A herbaceous twiner from 1.5–5 m long, growing over bushes or fences. Root horizontal, 1.5 cm in diameter, oval, flattened, seldom branched but marked on the upper surface with scars of previous years’ stems. Stems slender and twining. Leaves arranged differently according to their position—basal leaves sometimes in fours, middle section leaves nearly opposite and upper leaves alternate. Leaf blades ovate with 7–11 ribs, downy and greyish beneath; base cordate, margin entire or wavy, apex pointed. Petioles nearly as long as the blade and dilated at the base. Inflorescence in drooping axillary racemes and panicles. Flowers very small, dioecious, greenish yellow. Male flowers grow in elongated panicles, have 6 stamens and a minute, abortive ovary. Female flowers grow in racemes, with 6 abortive stamens and an oblong, sharply triangular 3-celled ovary. Fruit an oval, 3-celled, 3-winged membranaceous pod. Seeds winged, 2 in each cell.

Habitat

Indigenous to North America, in wet woods and swampy ground, from Canada and New England to Wisconsin and southward but is common only in the south. It is collected in the wild.

Parts used

The fresh root and rhizome collected in autumn. Grieve states that the herb must be harvested in the first year to prevent loss of its therapeutic value.

Active constituents1

1) Phytosterols including β-sitosterol, campesterol and stigmasterol2

2) Steroidal saponins (up to 0.4%) including diosgenin (glycoside = dioscin) (up to 3.5%) and protodioscin3

3) Alkaloids

4) Flavonoids based on flavan-3-ol3

Also contains tannins, mucilage and starch.

Nutritional constituents

Vitamins: C and A

Minerals: Calcium, chromium, magnesium, phosphorus, potassium and sodium

Actions

1) Anti-inflammatory

2) Spasmolytic

3) Cholagogue

4) Mild diaphoretic

5) Antirheumatic

Scientific information

The steroidal saponin, diosgenin, from Dioscorea spp. had become a predominant source of starting material for the manufacture of steroidal drugs including corticosteroids and sex-hormones.4 Initially Mexican yam was the main plant used, to the extent that it was nationalised by the Mexican government, its harvesting and processing leading to substantial changes in the lives and economy of people in that country.5 The price of Mexican yam escalated and alternate species were sought in other countries. Trigonella foenum-graecum is a more recently established source of diosgenin.6

Dioscorea spp. are found in the nutritional and medicinal tradition of many countries and their uses bear many similarities. Research has been conducted on a number of different species and on diosgenin but not a great deal has been published on the whole extract of D. villosa.

Hormonal

In vitro—The herb has an anti-oestrogenic activity7 but failed to have much effect on the hormone receptor sites in breast cancer cells.8

In vivo—A cream containing Dioscorea was used to treat menopausal symptoms in otherwise healthy women and found to have no effect on hormone or lipid levels, blood pressure and weight and no significant reduction of menopausal flushing or sweating.9 It has been suggested that extracts with a diosgenin content of less than 3.5% have no oestrogenic activity.1

A supplement containing Dioscorea was given to a group of older people and the effects on levels of dehydroepiandrosterone (DHEA) metabolites and lipid levels were monitored. Whilst DHEA levels were unchanged there was a favourable shift in serum lipids to reduce triglyceride and raise HDL levels.10

Other

In vitro—One of the flavan-3-ol glycosides has antifungal activity against Candida spp. including C. albicans.3

Disogenin

A good deal more research has been carried out on this constituent. In vitro studies show that it:-

It seems that diosgenin may be poorly absorbed however as serum levels of unmodified diosgenin were low after large doses were taken orally over a month.29

Medicinal uses

Cardiovascular system

Gastro-intestinal tract

Reproductive tract

Musculoskeletal

Pharmacy

Three times daily  
Decoction of dried root –   2–4 g
Tincture 1:5 (45%) –   2–10 ml
Fluid Extract (45%) –   2–4 ml

Precautions and/or safety

A report into the safety of the herb found it was not genotoxic in standard tests.1