An inventory of medicinal plants compiled by the WHO in 1978, that covered only ninety member countries, contained 20,000 species, of which only about 250 were of widespread use, and some of which had been analyzed to identify their main active chemical compound(s). Even this partial sampling reflects the enormous empirical traditional knowledge about medicinal plants. Most of this knowledge is verbal and some of it, if at all, was incompletely incorporated in historical and folkloric works. This traditional and local knowledge is the fruit of centuries and, in some cases, millennia of experience in plant use. South America, Africa, India, China and a few other countries like Burma, Sri Lanka, Philippines, Indonesia, Nigeria, Mexico, etc., are the treasure house of this knowledge. Only India and China have elaborate systematic records, but of a fraction of the uses of plants as medicine.

In this period of rapid transport, and multimedial communication, the accelerated process of acculturation destroys ancient values and practices. It also rapidly spreads epidemic diseases caused by micro-organisms, against which indigenous populations have no defense. These twin factors have brought about the extinction of certain tribes and with them their knowledge. A review of the texts of the first latin-American histories, has shown that since the discovery of the New World, hundreds of communities and tribes have disappeared (Naranjo, 1995). Currently, the progressive penetration of civilization into the immense Amazon region is causing the same effect as elsewhere in Africa and Asia, and is relegating ancestral knowledge to partial or total oblivion. Finally, the unconquerable and at times irreversible transformation of ecosystems, the degredation of extensive natural areas, and other factors have led to disappearance of many species. For example, of the thousands of Mexican medicinal plants cited by Hernandez (1959) from the sixteenth century records, many can no longer be found. A Similar situation exists in the rest of the developing world. The most urgent need is to rescue and record all traditional knowledge on plants, that possibly can be, as quickly as possible; and to save the natural vegetation from further degradation.

4 UTILITY OF PLANTS IN CONTEMPORARY MEDICINE

A large number of very specific pharmaceutical products, many of them synthetic, are available to treat almost every disease. Nevertheless, plants still have a pre-eminent place in today’s therapy, for the following reasons:

a) There is renewed interest in using plants in therapy as is the case with Artemisia annua, for the Chinese anti-malarial drug artemisin and species of Cinchona for quinine. With the therapeutic success of chloroquine and its synthetic derivatives in the treatment of malaria, the use of quinine passed into history of medicine. Through acquired resistance, an established biological phenomenon, pathogens and parasites can develop heritable resistance to chemotherapeutic agents on continued exposure, by a process of selection that results in acquiring resistance to a particular chemical compound (Gottlieb, 1982). This process has occurred, in part, with species of Plasmodium, the causative agent of malaria. Now the synthetic antimalarial drugs have lost such a significant part of their efficiency, in the last quarter of the twentieth century, that it has often been necessary to return to the use of artemisin or quinine. Currently, the surge in demand for these natural products is beyond the production capacity of the extraction laboratories. As a result, malaria has again become a great health risk in tropical areas (Naranjo, 1995). This demand has also been accentuated further by the acquired resistance of the insect vector, the Anopheles mosquito, to insecticides that were indiscriminately used in the twentieth century in sanitation campaigns.

Similar is the case with tuberculosis, where the therapy that was successful for a long time now suffers from the pathogen’s acquired resistance. There is an urgent need to find effective drugs also against this disease.

b) Modern medicine depends on a number of plants that are also used in traditional medicine, although they have not yet been improved upon. Neither all natural compounds can be totally artificially synthesised nor all the synthesised compounds are even equal to the natural product. Digioxin from Digitalis purpurea and Digitalis lanata could not be synthesised, and synthetic vincristine (of Cathranthus roseus) has been found to be far less efficient than the natural product (Pearce and Moran, 1994). Even if biotechnological procedures, involving micro-organisms to synthesise or modify therapeutic chemicals are employed, they function only on the base of a natural product (Principe, 1989). As is well known, synthetic chemistry has until now had little success in obtaining drugs effective in the treatment of various viral diseases. Even though immunotherapy has achieved great success, we still do not have vaccines for all viral diseases (Naranjo, 1995). It is possible that plants would be useful to treat viral diseases as several plant species of promise exist, as for example neem. Most antibiotics still come from fungi, and there is a vast scope for this in higher plants.

Before the hope in medicinal plants is realised, it is essential that that controlled studies are needed, for example, by the double blind system, to confirm their therapeutic effect. Nonetheless, in folk medicine these plants are employed with apparently favourable results, and above all without causing detectable unfavourable side effects.

c) Some plants are useful as co-adjuvants of other treatments. These plants can help in the treatment of certain diseases, even though there already exists a basic recommended medicine. The numerous Ayurvedic formulations containing several species of plants are examples of adjuvants, where only one or two (or few) species are the main ingredients.

d) Plants are useful in the treatment of mild afflictions that are common and frequent, such as the simple common cold and mild stomach ache or diarrhoea. These and other illnesses pass with little or no treatment; hygienic and dietary measures help. Infusions or decoctions of some plants, like garlic, pepper, cumin, ginger, etc., are well known in folk medicine throughout the world, to provide relief from these afflictions. These remedies can contribute to improving the general state of the patient.

4 DISCOVERY OF NEW THERAPEUTICALLY ACTIVE MOLECULAR MODELS IN PLANTS

Chemists now possess an enormous technical potential to obtain from a single basic molecular structure, a very large number of derivatives, each with a different side chain, all of which give the scope and hope of an unlimited proliferation of potential drugs. A single sulfa drug, discovered by Gerard Domagk in 1939, has yielded hundreds of synthetic drugs, although only some of them got to be used as medicine. The fundamental aim now, though often difficult to realise, is to develop, from a naturally occurring molecule in therapeutic use, new basic molecular structures with appropriate therapeutic properties and minimal side effects or toxicity. Pharmacology has been