PROSEA, Introduction to Medicinals 3

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Introduction to Medicinals, volume 3

The general aspects of medicinal and poisonous plants were highlighted in the introduction of Prosea 12(1): “Medicinal and poisonous plants 1". These included definitions, subgrouping, role, phytochemistry, biological and pharmacological activities, therapeutical applications, botany, ecology, agronomy, harvesting, handling after harvest, processing, utilization, quality control, genetic resources, breeding, research and development, from plant to drug and prospects. The introduction of Prosea 12(2): “Medicinal and poisonous plants 2" provided more detailed information on quality control of herbal drugs. The focus of the introduction of the present volume is on conservation aspects of medicinal plants.

Choice of species

The choice of the genera/species covered in each of the 3 volumes on medicinal and poisonous plants has been somewhat arbitrary, although the 3 volumes essentially reflect the importance of species: the most important ones in Prosea 12(1), the least important ones in Prosea 12(3). This implies that on the whole the medicinal and poisonous plants treated in the present volume are less known. Generally, little or no information is available on their phytochemistry and pharmacology. However, several genera/species covered in this volume have recently attracted attention because of interesting pharmacological properties (e.g. Butea, Calophyllum, Galbulimima belgraveana, Gynura and Morinda). Others are poorly known in South-East Asia, but have at least some medicinal reputation outside the region (e.g. Ajuga bracteosa, Cecropia peltata, Cestrum nocturnum, Clusia, Cocculus, Hymenocallis, Kigelia africana, Leonotis nepetifolia, Ruellia tuberosa and Tecoma stans). The latter category comprises many species introduced in South-East Asia. In addition, some genera are unimportant in South-East Asia, but include species that are medicinally important elsewhere (e.g. Cynoglossum, Drosera, Gentiana, Melissa and Taxus).

Collection from the wild versus cultivation

In general, plant species used as a source of drugs receive high priority in conservation activity. The extent of the trade in drugs of plant origin is enormous and largely unmonitored, and harvesting from the wild predominates. Comparatively few medicinal plants are cultivated. It is estimated that 70-90% of material for medicinal use is collected from wild populations (Lange & Schippmann, 1997).

The need for conservation

A number of medicinal plant species have become rare due to thoughtless exploitation of the natural resources. Several species are close to extinction, e.g. Rauvolfia serpentina (L.) Benth. ex Kurz which has been included in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Particularly in India many plant species used in local medicine are threatened or even close to extinction.

Many countries of the world, including those of South-East Asia, do not have an inventory of their medicinal plants. Thailand, Malaysia and the Philippines recently started to make such an inventory. Lack of population data of species is prevalent. An assessment of threat is therefore difficult to achieve. However, such information is essential to conservation efforts. The greatest conservation threat is posed by the high demand for slow-growing, slow-reproducing, habitat-specific species. Any intended use of a wild species requires an effective management system and a legal framework based on sound scientific information. For plant species used as a source of drugs, the resource management plan must address the following aspects (Lange & Schippmann, 1997):

  • Assessment of threat according to the literature and experience of experts.
  • Collection of population data by field research.
  • Investigation of data on the biology of species: distribution, life form, habitat requirements, plant community aspects, growth rates, reproductive biology and breeding system.
  • Review of existing harvesting systems: plant parts used, detrimental collection techniques and socio-economic aspects.
  • Review of national regulations for the utilization in the source country.
  • Extent of wild-harvesting versus cultivation.
  • Review of volume of plant material harvested and traded.
  • Establishment of a management system: annual harvesting quota, seasonal restrictions, regional restrictions, restrictions to certain plant parts or size classes and domestication projects.
  • Installation of a continuous monitoring and re-evaluation system.

Conservation of medicinal plants is hampered by the fact that they form a very large and heterogenous group concerning growth habit, distribution, reproduction, phenology and ecological requirements. The diverse conservation needs of the species make it extremely difficult to develop a coherent conservation strategy for the commodity group as a whole.

Joint efforts for conservation

Coordinated international work on medicinal plant conservation on a global scale has only just started. The World Conservation Union (IUCN), the World Health Organization (WHO) and the World Wide Fund for Nature (WWF) jointly published “Guidelines for the conservation of medicinal plants" (1993). A joint programme of the United Nations Educational, Scientific and Cultural Organization (UNESCO), WWF and Royal Botanic Gardens Kew has launched the “Peoples and Plants Initiative". The “Directory for Medicinal Plant Conservation" (Kasparek, Gröger & Schippmann, 1996) lists more than 200 networks, organizations and projects in this field. To coordinate the various efforts in medicinal plant conservation worldwide, the IUCN Species Survival Commission established the Medicinal Plant Specialists Group in 1994. In all these programmes the term “medicinal plant" is applied in a very broad sense, covering also plants used in adjacent fields such as cosmetics or functional food products, because nowadays cosmetics and food products are developed to add certain biological effects (e.g. anti-ageing and antioxidant activities). The International Plant Genetic Resources Institute (IPGRI) furthers the conservation and use of genetic diversity, and may provide a logical framework to support, guide and lead the global effort to conserve medicinal plant species and for their sustainable exploitation.

Germplasm collection

In Asia organized efforts to collect and conserve germplasm of medicinal plants are rare. In most countries, no germplasm collection of medicinal plants takes place at all (Chomchalow in Chomchalow & Henle, 1993). Traditional cultivars and their wild relatives represent particularly valuable sources for e.g. resistance to diseases, and therefore need to be collected, evaluated and conserved.

Plant germplasm can be stored in seed genebanks and field collections (ex situ), or protected in its natural habitat (in situ). The first method of storage is only possible for species with seeds that do not lose their viability within a short time. Appropriate seed storage technologies have to be worked out for the different species. In-vitro culture of organs, tissues, cells and protoplasts may be suitable for species with recalcitrant seeds. The second method is appropriate for conservation, but existing field collections are often for exhibition purposes and do not cover the genetic diversity of the species concerned. Collections of medicinal plants in South-East Asia are present in Indonesia, Malaysia, the Philippines and Thailand, each consisting of a few hundred accessions. For ex-situ conservation, priority should be given to those plants whose natural habitats have been destroyed or cannot be conserved, or to plants which have become rare or extinct at the local level. In-situ conservation is the best method for conserving germplasm, but is only useful when conservation areas are large enough, well chosen and effectively protected. In-situ and ex-situ conservation complement each other in conserving a maximum of genetic diversity.

An important objective of genetic conservation is to make germplasm more easily available to breeders. Samples from germplasm collections should be freely available to professional plant scientists, but property rights should be respected.

Cultivation and breeding

In several tropical countries a kind of transition exists between plants raised by cultivation and those collected from the wild. Young plants are collected in the wild and then planted out in fields. This kind of production may be called “wild cultivation". Botanical drugs obtained in this way are traded as cultivated products (Lange & Schippmann, 1997).

Loss of genetic diversity may cause problems when attempts are made to domesticate medicinal plants. A well-known example is the genus Cinchona, the bark of which has been used for quinine extraction to treat malaria since the end of the 19th Century. Overcollecting led to a drastic decline of the natural populations in South America. Domestication has prevented Cinchona from becoming extinct, but the genetic variability became very narrow. Therefore conservation of the last wild stands of Cinchona is important for future breeding efforts (Lange & Schippmann, 1997).

Availability of land limits the large-scale planting of medicinal plants. Agroforestry may be an option, combining the cultivation of agricultural crops such as oil palm or rubber with medicinal plants. Enrichment planting with selected species is also possible, both in natural forest and in plantation forest. Tests with enrichment planting of Eurycoma longifolia Jack showed promising results in Malaysia, and cultivation trials in oil-palm plantations also indicate interesting possibilities (Azizol Abdul Kadir & Mohd. Ilham Adenan in Nair & Ganapathi, 1998).

It should be checked whether the cultivated plants have the same qualities as the mother stock from the wild, as qualities often depend on growing conditions. Large pharmaceutical companies have well-established laboratories and nurseries to study and grow economically important medicinal plants, but the results are often not freely available because of economic and commercial implications (Rao & Rao in Nair & Ganapathi, 1998).

Genetic improvement of medicinal plants has hardly begun. When plant breeders have exploited most of the available variability in a certain species they look for other sources of variability through hybridization with wild species. Some of the difficulties in breeding quantitative characters can be overcome by combining the traditional techniques with modern molecular techniques. These latter techniques can provide genes to traditional plant breeders from previously inaccessible sources (e.g. unrelated plant species, viruses and bacteria) (Nazmul Haq in Chomchalow & Henle, 1993).

Recommendations for the wise use of medicinal plants

According to IUCN, WHO and WWF (1993) the cultivation of plants as sources of drugs is the best and most promising way to satisfy the market’s expanding demand for these raw materials. For wild plant species that are endangered through overexploitation this is certainly the only method to stop their decline and to secure their long-term survival. However, as long as there is a lack of knowledge concerning efficient species-specific cultivation techniques, collecting in the wild will continue to play an important role.

In 2002 the Bonn Guidelines were adopted at the sixth meeting of the Conference of the Parties to the Convention on Biological Diversity. These guidelines were developed in response to growing concerns in many developing countries that the commercial and scientific gains realized from their genetic resources were being reaped only by bio-prospectors based in foreign countries. Although voluntary, the guidelines should improve the way foreign companies, collectors, researchers and other users gain access to valuable genetic resources in return for sharing the benefits with the countries of origin and with local and indigenous communities. This refers especially to medicinal plant resources. For the commercialization of natural resources, benefit sharing may be an incentive for their long-term conservation through local communities. To achieve conservation goals, commercial users of plant resources should incorporate the costs of sustainable use into their marketing calculations.

The medicinal and poisonous plants of South-East Asia in retrospect

In the three Prosea volumes on medicinal and poisonous plants about 1290 species are reviewed belonging to 548 genera. All genera have been rated concerning their medicinal importance (based on the text of the papers). The 269 genera valued as having regional or at least local medicinal importance are used for the determination of the most important families of medicinal and poisonous plants, and habit and habitat ratios (Tables 1, 2 and 3, respectively). They belong to 92 different families, illustrating the great diversity of South-East Asian medicinal plants. It should be noted that there are many more medicinally used plants in South-East Asia, but they have another primary use and are treated in other Prosea volumes (see chapter 3 on medicinal and poisonous plants with other primary use). The total number of South-East Asian medicinal and poisonous plants (with recorded uses in the literature) amounts to approximately 2200 species.

Some plant families comprise markedly more medicinal plants than others. Table 1 shows the 10 most important families in terms of number of genera with at least local medicinal importance treated in the Prosea volumes 12(1), 12(2) and 12(3). The weighted importance is determined by dividing this number by the total number of genera classified in the family in the Prosea Basic list of species and commodity grouping (Jansen et al., 1991), which is considered to level down the size of the family. However, families with many small genera in South-East Asia (such as Compositae) are probably underestimated and those with few but often large genera (such as Verbenaceae) overestimated. It is evident that Compositae is an important family of medicinal plants in South-East Asia, but smaller families such as Amaranthaceae, Labiatae, Menispermaceae and Simaroubaceae are also of considerable importance. This can be at least partly explained by the common presence of active compounds, such as sesquiterpenoid lactones in Compositae, essential oils containing phenolic compounds in Labiatae, bisbenzylisoquinoline and protoberberine alkaloids in Menispermaceae and quassinoids in Simaroubaceae.

Table 1. The 10 most prominent families of medicinal plants in South-East Asia and their weighted importance
Family Number of genera Weighted importance
Compositae 23 0.354
Leguminosae 22 0.158
Apocynaceae 14 0.292
Rubiaceae 12 0.164
Euphorbiaceae 11 0.167
Labiatae 10 0.435
Menispermaceae 10 0.667
Verbenaceae 9 0.391
Simaroubaceae 7 0.875
Amaranthaceae 6 0.600

Table 2 presents the share of the predominant habit of the genera with at least local medicinal importance treated in Prosea 12. Table 3 shows the share of the predominant habitat of these genera. It can be concluded from these tables that herbs of open, often disturbed habitats, which are often weeds, form the most important group of well-documented medicinal and poisonous plants in South-East Asia. Species restricted to a forest habitat account for a comparatively small share (31%) of the more important medicinal plants. This is a remarkable result considering the fact that forest is still the prevailing land cover in South-East Asia and comprises the most species-rich habitat types, being especially rich in woody species. It seems most likely that the high proportion of herbs from disturbed habitats amongst the more important medicinal plants is because they are so widely distributed and common that they are the most obvious plants to be tried for medicinal purposes. This also suggests that the forest in South-East Asia still accommodates a vast reservoir of potential drug species awaiting pharmacological investigation.

Table 2. Habit of more important South-East Asian medicinal and poisonous plants (in %).
Habit Proportion
Tree 18%
Shrub 26%
Liana 12%
Herb 44%

Table 3. Habitat of more important South-East Asian medicinal and poisonous plants (in %).
Habitat Proportion
Forest habitat (wild) 31%
Open habitat (wild) 59%
Cultivated 10%