Ethnobotany and conservation of medicinal plants

R.L.A. MAHUNNAH and E.N. MSHIU

Traditional Medicine Research Unit
Muhimbili Medical Centre
P.O. Box 65001
Dar es Salaam, Tanzania

ABSTRACT

Plants are indispensable to man for his livelihood. This paper presents the value of ethnobotany to the search for new biomedical compounds in the tropics. The general values of the rich tropical vascular plant flora as sources of direct therapeutic agents, as sources of starting points for the elaboration of more complex semisynthetic compounds, as sources of substances that can be used as models for new synthetic compounds, and as taxonomic markers for the discovery of new compounds, are highlighted. A case is made for continued research in ethnobotany, since it is estimated that 80% of the people in the Third World rely on traditional medicine for primary health care needs, most of which is plant-derived.

The whole question is addressed from socio-economic perspectives. Of all the plant-derived compounds that are used in the prescription drugs, about 50% originate from the tropics; yet it is here where the greatest threats to plant biodiversity occur. Therefore, concerted ethnobotanical research is directly linked to the urgent need for sustainable conservation programmes. It is proposed that conservation programmes for developing countries take into account both conservation of maximum plant biodiversity and focused approach aimed at individual medicinal plants.

The results should facilitate better management of our medicinal plant genetic resources for sustainable economic harvesting in both in-situ and ex-situ conservation -areas.

Introduction

Our purpose here is to urge that ethnobotanical prospecting, the exploratory process by which new useful plants are discovered, be substantially intensified. However, plant species are being lost at an ever-increasing rate, faster by orders of magnitude than rates of evolutionary replacement. Therefore intensification of ethnobotanical exploration should, of necessity, be linked to the urgent need for sustainable conservation strategies for medicinal plants since human expansionist demands can be expected to wreak environmental deterioration and biotic destruction well into the next century.

This paper specifically urges for an Increased involvement of developing nations in the exploratory and conservatory process, an involvement which, in our view, is warranted on scientific, economic and cultural grounds.

Traditional Therapy

Traditional medicine is a priceless heritage which was created in the historical course of prevention and treatment of diseases over a long period. Today, traditional systems of medicine, which utilize mostly plant-derived prescriptions, remain the source of primary health care for more than 3/4 of the Third World population. It is estimated that a third of all world pharmaceuticals are of plant origin, or if algae, fungi and bacteria are included, then two thirds of all pharmaceuticals are plant based. Therefore, traditional medicine and medicinal plants are indispensable in practice. The rich traditional ethnopharmacopoeia of the Third World's tropical flora is, indeed, indicative of the high utility of indigenous medicinal plants.

Proper development and utilization of traditional medicinal plants, is of great significance in the development of health services and provides for proper take- over of national cultures for developing countries. The merit of traditional therapeutics cannot be over-emphasized. It is easily acceptable to the community, manageable and is of low cost. With the rich traditional medicinal plant resources, efficacy of prevention and treatment of disease can be ensured by appropriate, but comparatively non-sophisticated technology and with minimal side effects. Therefore proper utilization of the traditional medicinal systems by developing nations can make significant contributions towards the implementation of the programme of Health For All by the year 2000.

Drugs from nature

Through most of man's history, botany and medicine were, for all practical purposes, synonymous fields of knowledge. Therefore, the traditional healer, usually an accomplished traditional botanist, represents, probably, the oldest professional man in the evolution of human culture. However, the advent of modern technology and synthetic chemistry has been able to reduce our almost total dependency on the plant kingdom as a source of medicine. Nonetheless, plants have traditionally served as man's most important weapon against pathogens. In fact, it seems that even the Neanderthal man knew and made use of medicinal plants.

What, then, is the value of ethnobotany to the search for new biomedical compounds? Of the hundreds of thousands of species of living plants, only a fraction have been investigated in the laboratory. This poor understanding of plants is particularly acute in the tropics. Consequently, this calls for the urgent need for continued ethnobotanical research. The importance of ethnobotanical enquiry as a cost-effective means of locating new and useful tropical plant compounds, cannot be over-emphasized. Most of the secondary plant compounds employed in modern medicine were first 'discovered' through such investigation. Some 119 pure chemical substances extracted from higher plants, are used in medicines throughout the world, and 74% of these compounds have the same or related use as the plants from which they were derived. The rosy periwinkle, Catharanthus roseus (synonymous to Vinca rosea), represents a classic example of the importance of plants used traditionally by man. This herbaceous plant, native to South-eastern Madagascar, is a source of over 75 alkaloids, two of which, vincristine and vinblastine, are used to treat childhood leukemia and Hodgkin's disease, with a significant success rate. The use of quinine from Cinchona bark to cure clinical malaria, today owes its use by Peruvian Indians in the 17th Century, who employed crude extracts from the Cinchona trees to cure malarial fevers. These are but only a few of what modern medicine owe to ethnobotanical treasures.

There are four basic ways in which plants that are used by tribal peoples are valuable to modern medicine. First, some plants from the tropics are used as sources of direct therapeutic agents. For example, the alkaloid D - tubocurarine, extracted from a liane, Chondradendron tomentosum, is widely used as a muscle relaxant in surgery.

Secondly, tropical plants provide sources of starting points for the elaboration of more complex semi-synthetic compounds. For example, saponin, an extract from Dioscorea, is chemically altered to produce sapogenins, necessary for the manufacture of steroidal drugs. Thirdly tropical flora can serve as sources of substances that can be used as models for new synthetic compounds. Cocaine from the plant Erythroxylum coca, has served as a model for the synthesis of a number of local anesthetics, such as procaine. Lastly, plants can also be used as taxonomic markers for the discovery of new compounds. For example, although little was known of the chemistry of the Orchidaceae, plants of this family were investigated because of its close systematic relationship to the Liliaceae. The research demonstrated that not only was the Orchidaceae rich in alkaloids, but many of these alkaloids were unique and thought to be of extreme interest for the future. This rich natural economic resource needs urgent appraisal to coincide with the current "green wave" of lay interest in herbs and natural plant medicines, which is unparalleled in modern history.

We must consider seriously the importance of medicinal plants in the developing countries. The World Health Organization estimated that 80% of the Third World population rely on traditional medicine for primary health care needs. In many cases, these countries simply cannot afford to spend millions of dollars on imported medicines which they could produce or extract from their tropical forest plants. Indigenous medicines are relatively inexpensive; they are locally available and are usually readily accepted by the people. The ideal situation would be the establishment of local pharmaceutical firms that would create jobs, reduce unemployment, reduce import expenditures, generate foreign exchange, encourage documentation of traditional ethnomedical lore, and be based on the conservation and sustainable use of the tropical forests.

Conservation

What can the medical community do to aid both the struggle to conserve tropical forests and the search for new plant medicines? Many reasons have been presented to the general public: aesthetic, ethical and the like. But the most relevant to the medical profession is the utilitarian, that is, species are of direct benefit to us. The few examples that are given above (drugs from nature), are indicative of the kinds of undiscovered compounds that are undoubtedly there to be discovered.

Tropical forests are complex chemical storehouses that contain many undiscovered biomedical compounds with unrealized potential for use in modern medicine. We can gain access to these materials only if we study and conserve the plant species that contain them. The point that cannot be over-emphasized, and which is at the core of our argument here, is that biotic impoverishment is tantamount to chemical impoverishment. Loss of a species means loss of chemicals of possible use, chemicals potentially unique in nature, not likely to be invented independently in the laboratory.

Clearly, the most urgent conservation problems are occurring in the tropics. While the tropical forests cover less than 10% of the earth's surface, they are believed to contain over 50% of the world's species, and the majority of the endangered species. Extinction is a natural process, yet to view these recent extinctions as natural, is to misinterpret the geological record.

Parallel to this, is the urgent need to document and conserve ethnomedical plant lore, since indigenous knowledge is essential for use, identification and cataloguing of the (tropical) biota. As tribal groups disappear, their knowledge vanishes with them. Thus, the preservation of these groups is not a luxury, but a significant economic opportunity for the developing countries. Failure to document, this lore would represent a tremendous economic and scientific loss to humanity.

Action plan

To achieve these objectives ultimately, some practical issues need to be addressed to. These include:

(a) Formulating clear policies on the practice of traditional medicine. The policies should promote, inter alia, the organization of traditional healers, and realistic integration of traditional and modern medical practices.

(b) Promoting the volarization of medicinal and aromatic plants growing in the spontaneous flora, by setting up specialized units in agrobiological, pharmaceutical industrial and quality control aspects.

(c) Promoting the strengthening of research capability in the field of traditional medicinal plants.

(d) Promoting research in the economic mapping of the indigenous vascular plant flora, to identify the qualitative and quantitative natural resources, in medicinal and aromatic plants, in order to render the economic potential profitable.

(e) Promoting ethnobotanical studies to retrieve the vanishing ethnomedicinal information from remote village communities especially the traditional healers.

(f) Promoting the conservation of medicinal and aromatic plants, based on realistic in situ and ex-situ sustainable programmes, i.e., conservation of maximum plant biodiversity and individual plant species, respectively.

(g) Promoting meaningful infra-regional, regional and international cooperation that will enhance the exchange of information and technology of medicinal and aromatic plant genetic resources, without jeopardizing the genetic germ plasm.

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