Genetic diversity often falls into patterns that characterise subgroups, within a species, which have distinct economically valued traits. A number of crop plant species have, in addition to the scientifically recognised varieties (cultivars), a large number of local genetically different variants over the range of their geographical distribution/cultivation. These are, often ambiguously, called races or land races, occur in an unestimably large numbers in the case of the widely cultivated crops like rice, wheat, bajra, jowar, etc. The enormity of the problem in handling genetic variability should be evident from the existence of over 1,00,000 varieties of rice, over 15,000 varieties of the common bean and 12,000 of the potato. The genetic variability of cultivated species/varieties and their wild relatives, together forms a continued basic supply of traits for breeding new and improved varieties and for this reason these are called the ‘genetic resources’ of a country/region. A similar situation, largely unexplored and unexploited, though may be of a lesser magnitude, exists also in other plant species, including the medicinally important ones.

       In the case of medicinal plants, it is known that populations of a particular species from certain localities have been traditionally preferred. There are no systematic studies on medicinal plants with reference to gene based differences in the production of therapeutically active chemical constituents, but there are several indications. For example, a therapeutically useful lectin (a specific class of protein, detailed in a later chapter) from the seed of Jack fruit (Artocarpus heterophyllus) showed 2,500 times more activity in a sample from Bangalore, than in a sample from Madras (Hunter, 1986). This is one aspect of chemical diversity, a component of genetic diversity. Studies on chemical diversity, both quantitative and qualitative, on medicinal plants are largely absent and very much needed.

      In view of these considerations, it seems necessary that at least the important and the more commonly used medicinal plants are studied systematically with reference to their genetic diversity.

      May (1990) wrote that "without taxonomy to give shape to bricks and systematics to tell us how to put them together, the house of biological science is a meaningless jumble". Taxonomy is the foundation of the study of biodiversity.

      There are no differences in the taxonomic procedures, practices and nomenclature between medicinal and nonmedicinal plant taxa. If the medicinal plant is a cultivar of a crop plant species, then some differences exist, at the level of the cultivated varieties (cultivars).

     In general, the Indian medicinal plants require a thorough taxonomic handling a) for their accurate botanical description and taxonomic determination, and b) to understand the magnitude of their diversity and usefulness, and c) to determine the need for and extent of conservation.

       There has been a rapid decline in the biodiversity of the world, more particularly during the past two decades or so. Biodiversity losses have been alarming in the developing countries in the tropics. For example, in the Uttara Kannada district of Karnataka, the forest area has come down from 8,000 sq km to 6,000 sq km, in about 40 years (Potter, 1996). This constitutes an enormous loss of biodiversity in a small area over a short period of time. There are innumerable such examples, the world over. The underdeveloped countries are generally less aware of the degree of biodiversity loss in their countries and its consequences.

       Biodiversity losses occur due to habitat destruction, over harvesting, pollution, inappropriate and often accidental, introduction of exotic plants and animals, etc. Habitat destruction is often related to development projects like land conversion, construction of dams, etc. Biodiversity is also lost due to sudden natural calamities like floods, cyclones, hurricanes, earth quakes, etc. Conservation of biodiversity is one of the paramount concerns the world over. Governments, nongovernmental organisations (NGOs), scientists, are all preoccupied with the problem of devising ways and means of conserving biodiversity, or at least retarding the rapid rate of its loss.

       There have been several estimates and projections of the loss of world’s biodiversity. Since most of habitat destruction is through human activities, these are the basis of most calculations.

       Of an estimated 17,444,300 square kilometers of primary vegetation in 25 of the world’s hotspots (explained later on), only 2,122,891 square kilometers of vegetation exists now, constituting 12.5 per cent of the original vegetation (Myers et al., 2000). This is one dimension of the magnitude of biodiversity loss.