LEGUMES

The Story of Chinese Medicinal Plant Resources

by Subhuti Dharmananda, Ph.D., Director, Institute for Traditional Medicine, Portland, Oregon

PLANT DIVERSITY AND MEDICINAL RESOURCES IN CHINA

It has been estimated that there are more than 30,000 plant species in China (1). Of these, about one-third are used as sources of medicinal plants (approximately 11,000); this is a huge proportion of the available species. This statistic helps reveal the extent to which the Chinese have utilized their plant resources. Among the species of medicinal plants, some are mainly confined to folk medicine and some are used as occasional or local substitutes for the main species listed in the Materia Medica. About half of all the species used medicinally (more than 5,000) are listed in the 10 volume Illustrated Record of Chinese Materia Medica published in 1991 (4).

Despite these huge numbers of medical plants, only about 1,200 (about 10%) of the total medicinal species actually represent the standard Materia Medica items-including the more commonly used substitutes for them-that are learned by Chinese pharmacists and herbal prescribers. In the book Oriental Materia Medica (6), published in English in 1982, there are over 750 entries, of which about 600 are plant materials used in China, with an average of 2 source species per entry, or about 1,200 species. The book Thousand Formulas and Thousand Herbs of Traditional Chinese Medicine (5), published in English in 1993, has about 1,000 entries, of which about 850 are derived from plants, though there is only one botanical species mentioned for each entry, with a total of 800 plant species (some species yield multiple medicinal materials described separately). These texts, with information relating to 800-1,200 species of plants, represent the mainstream of traditional herbal practice as it occurs today in China, with English language presentation that makes them suited to study worldwide.

In the U.S., students of Chinese medicine enrolled in colleges of Oriental Medicine frequently rely on the book Chinese Herbal Medicine: Materia Medica (10) for background information about Chinese herbs. This book presents only about 470 entries, of which about 370 are plants. Usually, a single species is mentioned for each, though for some entries as many as four species are mentioned; in all, about 500 different plant species are included. Several hundred species, including some prominent Materia Medica items, are missing compared to the more comprehensive English language listings. Western students of Chinese medicine are not expected to learn the botanical names of the medicinal materials. Indeed, discussion of substitute species, or about where to locate information on other items of the larger Chinese Materia Medica, are not part of the curriculum. As a result, most Western practitioners remain unaware of the scope of Chinese herbal medicine and some of the issues that are related to botanical sources.

COLLECTION, CULTIVATION, AND USE OF CHINESE PLANTS

Each year, China produces about 3 million tons of dried medicinal plant materials, most of it used in China and in neighboring countries that practice Chinese medicine. About 10% of the Chinese dried plant material used in the practice of herbal medicine comes from cultivation, the remainder is obtained from wild supplies. According to a survey of medicinal materials (3), about 100 species of medicinal plants are under cultivation, utilizing some 460,000 hectares (more than one million acres) of land, and this effort is increasing rapidly. Several of the most commonly used herbs are cultivated to meet the large demand for them. Among the intensively cultivated plants are ginseng, tien-chi ginseng, codonopsis, astragalus, tang-kuei, coptis, rehmannia, moutan, cinnamon, cardamon, and atractylodes. Medicinal mushrooms are increasingly cultivated and even grown as mycelial cultures in liquid media.

In China alone, there are about 1,300 factories that produce prepared herbal medicines (with about 4,000 different formulas), and 2,170 hospitals in which traditional Chinese medicine is practiced (as of 1995). For perspective, ITM utilized about 50 tons of dried medicinal plant materials (in the form of powdered herbs and as concentrated dried extracts of the herbs) in one year to make its Seven Forests herb formulas, which are estimated to represent about 5% of the U.S. utilization of Chinese herbs provided via health professionals. Thus, a total of about 1,000 tons (0.03% of the Chinese production) is used for medicinal Chinese herb formulas in the U.S., though considerably larger amounts of Chinese herbs are provided direct to the public in products based on ginseng and a few other popularized herbs. There are about 6,000 health professionals in the U.S. that prescribe Chinese herbs as a regular part of their practice; most of these practitioners prescribe relatively low dosages of herbs compared to levels described in the Materia Medica books. By contrast, there are approximately 35,000 students of traditional Chinese medicine enrolled in schools in China and over 250,000 practitioners, most of them prescribing relatively high doses of herbs.

LEGUMINOSEAE (LEGUMES)

There are about 220 families of plants in Southeast Asia. The plant family known as the Leguminoseae is one of the major sources of both foods and medicinal herbs in China and throughout the world. Most of the food products are commonly known as "legumes:" the very wide variety of beans, the smaller group of peas, and the peanuts. Generally, it is the seed (bean) that is consumed as food; in a few cases, such as snow peas and green beans, it is the seed with pod. Rarely, other parts of the Leguminoseae plants are used in foods, such as the starch obtained from kudzu root (pueraria) that is important in Japanese cuisine. Most of the legume seeds are valued as sources of protein and constitute one of the main non-animal proteins in the diet. Some legume seeds are used as sources of oil, such as soybean oil and peanut oil.

A food that was initially widely-used only in the Orient, but is now recognized worldwide as having medicinal benefits, is soy beans (see: Soybeans for health). In terms of health and nutrition, these beans are valued for their oils (especially the component lecithin), vitamins (soybeans are the main source of natural vitamin E, also obtained from the oil), protein (soy protein is considered one of the most balanced sources of essential amino acids in the plant world), and their flavonoids (of which genistein has been most often mentioned in recent literature; daidzein is present in similar amounts and was studied earlier after isolation of it from pueraria). But soy is only one of many legume foods that is used for medicinal purposes in the Orient. In the book Vegetables as Medicine (7), other legumes listed include broad beans, mung beans, rice beans, sword beans, black-eyed peas, cow peas, black and green gram (dahl), kudzu (pueraria), peanuts, and coffee senna (cassia).

Worldwide, there are a total of 790 genera and 17,600 species of the legumes (5); of these, there are 163 genera and 1,252 species that are used as sources of medicinal plants in China. The legumes include trees, shrubs, and small herbs. Among the sources of Oriental herbal medicines, the Leguminoseae is the fourth largest family in terms of numbers of medicinal genera and species that are used, following the Gramineae (grasses, grains), Compositae (daisies, dandelions), and Orchidacea (orchids). However, in terms of total amount of medicinal material collected and used, the Leguminoseae rates at or near the top, thanks to the heavy reliance on astragalus and licorice in modern practice of Chinese medicine.

In terms of the more commonly used materials from this plant family, the Illustrated Dictionary of Chinese Medicinal Herbs (9) lists nearly 100 genera and 280 species of legumes. Hu Shiuying listed 60 genera of legumes, with nearly 100 species in her extensive book An Enumeration of Chinese Materia Medica (8). About 30 genera of legumes are described in Oriental Materia Medica (see Table 1), representing the main ones used by practitioners of Chinese medicine.

The Leguminoseae can be divided into three subfamilies (based on flower structures), of which the Papilionoideae is by far the largest source of medicinal plants. The much smaller Mimosoideae subfamily (of which the mimosa tree, known for its touch-sensitive leaves, is a representative) includes abrus, acacia, mimosa, and albizzia, of which only the last is somewhat frequently used today (the bark of albizzia is the main part used, but the flower as also been adopted). The Caesalpinioideae (of which the brasil tree, Caesalpinia sappan, is representative), includes cassia, gleditsia, and sappan, all of which are used with low frequency, but are generally known to herbalists (cassia seeds and leaves are used; gleditsia fruits and stem spines are used). The Papilionoideae subfamily includes the rest of the major herbs, mainly weeds, shrubs, and vines, several of which are well-known to Western practitioners of Chinese medicine, such as astragalus, licorice, pueraria, and sophora.

For each item of the Materia Medica that derives from the Legume Family, there are sometimes several species belonging to a single genus, used more or less interchangeably. For example, it is reported (2) that there are 7 species of Astragalus used for huangqi (astragalus root) and 6 species of Glycyrrhiza used for gancao (licorice root). In a few cases, there are several genera of legumes used as sources for the same herb. For example, the Chinese herb jixueteng is commonly derived from three genera-Spatholobus, Mucuna, and Millettia-of the Leguminoseae, and there are about a dozen species that are relied upon for source materials (see: Millettia (Jixueteng)). Although "millettia" has been adopted as the English common name for the herb (the dominant species traded in Hong Kong is from the genus Millettia), currently, one of the species from another genus, Spatholobus suberectus, is most widely used in China.

Several species of legumes are cultivated (3). These include Astragalus sinensis (root), Cassia acutifolia (senna leaf), Cassia obtusifolia (cassia seed), Dolichos lablab (seed), Gleditsia sinensis (fruit and spine), Glycyrrhiza uralensis (licorice root), Psoralea corydifolia (fruit), Sophora japonica (flower bud), and Trigonella foenum-graecum (fenugreek seed). At this time, none of the medicinal legume species are on the international endangered species list; legumes are tenacious plants that are not easily eradicated. The wild pea, for example, is often considered a nuisance plant and the kudzu vine has actually been destructive in the southern U.S. (it can overgrow structures and tear them down) where it was planted years ago for erosion control.

TABLE 1: Herbs from the legume family of plants, with actions according to Oriental Materia Medica, except items with a star (*) which were described in Thousand Formulas and Thousand Herbs of Traditional Chinese Medicine.

MEDICINAL INDICATIONS, ACTIONS, AND ACTIVE CONSTITUENTS

A close examination of the medicinal herbs in this plant family reveals that a number of the herbs have traditional indications in common (see Table 2). The frequently mentioned effects of the herbs, from the traditional perspective, are:

1. dispelling heat, cleaning toxins, resolving swellings;
2. removing water accumulation;
3. opening meridians, vitalizing blood, controlling pain;
4. controlling bleeding; and
5. resolving phlegm accumulation, cough, and lung disorders.

The ability of the herbs to clear heat and clean toxin may be due, in large part, to antiseptic and antiviral activity of the flavonoids, saponins, and alkaloids generated by this family of plants. The swellings that are resolved may be those that result from internal infections; thus, this quality may also represent anti-infection activity. Anticancer properties have also been noted, especially with the Sophora species and the folk remedy trifolium, so swellings that represent tumors might also be affected by appropriate selection and application of the herbs.

The blood-vitalizing activity of the herbs has been attributed to the flavonoid components. Thus, for example, the following is a summary of the actions of pueraria root (3):

A chemical study of this plant yielded a series of isoflavones, daidzein, daidzin, puerarin, and other compounds. Pharmacological studies demonstrated that the total isoflavone fraction from the plant was capable of increasing both cerebral and coronary blood flow, decreasing the blood oxygen consumption of the myocardium, increasing the blood oxygen supply, and depressing the production of lactic acid in oxygen-deficient heart muscle. It also demonstrated a papaverin-like spasmolytic action [that is, it can relax arterial muscles]. Daidzein and puerarin showed pharmacological actions similar to those of the total isoflavone fraction. Clinical trials of the preparation made from isoflavone extracts or daidzein have been shown to alleviate the symptoms of hypertensive disease, including headache and dizziness. It was efficacious against angina pectoris, migraine, and sudden deafness. As a result of these trials, the total isoflavone preparation was developed [as a standard product]....

The ability of some of the herbs to control bleeding may also be attributed to flavonoids, many of which strengthen the blood vessels, and the saponins may contribute to resolving phlegm accumulation. Other properties of the herbs, such as diuretic effect, are not yet explained by known constituents. The Leguminoseae produces little in the way of aromatic components (essential oils); no species of this family were mentioned in the Chinese reference guide Aromatic Plants and Essential Constituents (11).

A careful further study of plants within the Legume family that have similar properties may help reveal the manner in which certain groups of active constituents can explain the traditionally attributed herbal effects. Recently, a number of legume plants have been utilized specifically for the treatment of immune-deficiency caused by cancer therapies (or other medical interventions, such as radiation therapy), most notably astragalus, millettia, psoralea, and licorice; these and others from this plant family have been used to counteract other toxic effects of drugs (see: Counteracting the side effects of Western medical therapies). The mechanism of action has not been fully elucidated and a comprehensive study of the chemical constituents and pharmacology is needed to determine whether these components from the same family of plants share common structure-function relationships.

Table 2: Summary of commonly-cited herb actions for the legume family plants. Included are a few modern indications for some of the herbs, such as using pueraria to vitalize blood circulation, which are not mentioned in Oriental Materia Medica.

REFERENCES

1. Kuipers S, International summit on drugs from natural products, Herbalgram 1996.
2. Xu Guojun and Wang Zhengtao, Advances of pharmacognosy in China from 1985-1988, ACME 1989; 3(4): 398-413.
3. Liu Changxiao and Xiao Peigen, An Introduction to Chinese Materia Medica, 1993 Beijing Medical University Press, Beijing.
4. Zhonggui Bencao Tulu [Illustrated Record of Chinese Materia Medica], 1991, Beijing.
5. Ling Yeou-ruenn, A New Compendium of Materia Medica, 1995 Science Press, Beijing.
6. Hong-Yen Hsu, et al., Oriental Materia Medica: A Concise Guide, 1986 Oriental Healing Arts Institute, Long Beach, CA.
7. Chang Chao-liang, et al., Vegetables as Medicine, 1989 The Ram's Skull Press, Kuranda, Australia.
8. Hu Shiuying, An Enumeration of Chinese Materia Medica, 1980 Chinese University Press, Hong Kong.
9. Wee Yeow Chin and Hsuan Keng, Illustrated Dictionary of Chinese Medicinal Herbs, 1992 CRCS Publications, Sebastopol, CA.
10. Bensky D and Gamble A, Chinese Herbal Medicine: Materia Medica, 1993 rev. ed., Eastland Press, Seattle, WA.
11. Zhu Liangfeng, et al., Aromatic Plants and Essential Constituents, 1993 Hai Feng Publishing Company, Peace Books, Hong Kong.