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In the wilderness of the tropics, plants grow in extreme situations along longitudinal, latitudinal and temperature gradients and therefore variations within and between populations of a species are not uncommon. Although plants in general show habitat and distribution preferences, there are many a species which are neutral and adapted to other environmental regimes. Much of the variations in phenotype observed in natural populations of a species were earlier attributed to environmental influences (Briggs and Walters, 1984). Thus individuals of a species adapted to a particular soil type and climatic zone were designated as edaphic ecotypes and climatic ecotypes respectively. Many botanists reasoned that distinct intraspecific variations of plants were merely due to habitat modifications and adaptation to environment was by phenotypic plastic response. Phenotype was accepted as a resultant product of interaction between genotype and environment and different phenotypes of a given genotype could occur in different environments. Since a plant remains static and possesses persistent meristems and succession of organs of limited growth, it was thought to show greater phenotypic variability than a higher animal.

In certain plants developmental variations were observed as evident from differential morphological characteristics of the juvenile and adult forms. In early 1920s, the European botanist Turesson added yet another dimension to the problem of variations by demonstrating the persistence of morphological variations in the same species under standard conditions of cultivation (Turesson, 1922 a, b). The results of his ingenious experiments proved beyond doubt the widespread occurrence of intraspecific, habitat correlated genetic variations. It was soon realized that adaptation to environment was sometimes by plastic responses but more frequently had a genetic basis. Since selection operated in natural populations, well-adapted genotypes were thought to be selected preferentially over others in each habitat.

The problem of variations is further compounded in medicinal plants which apart from displaying visible variations, synthesize and accumulate an array of plant-specific chemicals. These compounds together called secondary metabolites are mostly high-value, low-volume compounds biosynthetically derived from primary metabolism and accumulated by certain plants or groups of plants in trace quantities. In plants 'defense chemicals' form a therapeutic arsenal to fight a variety of biotic and abiotic stresses. A study of variation in the active principles is often an important element in the investigation of variation in such plants. Although only limited number individuals in a plant population were usually subjected to chemical scrutiny to represent the population of a taxon in earlier studies, subsequent investigations brought out significant variations within as well as between populations. Thus it became reasonable to assume that chemotypes or chemical variants occurred in wild populations of medicinal plant species.

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