Q. Show the process of Chemotaxonomy ?

Chemotaxonomy is a science which uses chemical information as a character for taxonomic purposes. Before we analyse the basis of this modern trend in plant taxonomy, let us for a moment think about the different kinds of plants in our daily lives. When we drink tea or coffee, we appreciate the flavour or aroma and differentiate the two by this character. Similarly, when we eat fruits such as the mango, the banana or the apple, we find that they taste differently. This difference is due to the chemical constituents of these foods and this forms the basis of chemotaxonomy where the chemical features or chemical constituents serve as the evidence for taxonomy. The potential importance of chemical evidence in plant taxonomy has been suggested by both botanists and chemists and this has become an important recent trend especially because newer techniques for quick analysis of plant I material have been developed. Chemotaxonomists suggest that chemical characters I have a particularly high taxonomic value because they are i) stable, ii) unambiguous, and iii) not easily (if at all) changeable. Further, chemical characters will show chemical relationships amongst plants in the same way as morphological characters show morphological relationships.

Although chemotaxonomy is considered to be a relatively recent development in modem taxonomy, its origin can be traced to very early classical taxonomy. You will recall that the spice plants were identified on the basis of their aromatic properties, or the medicinal plants by their curative value. These aromatic properties or the curative value was largely based on the chemical constituents of the plants and taxonomists have classified them since ancient times using these chemical features along with morphological characters. However, it is only in recent years that chemotaxonomy as an important field of study has been established.

A review of the large amount of literature published in this field reveals that chemical data may be obtained from any part of the plant. Secondly, depending on the purpose of the investigation, the chemical information may be used for description or identification of plants, or for establishing relationships. This evidence assumes greater significance when it is used to sort out differences in taxonomic relationships when 2 or more possibilities are suggested on the basis of morphological characters.

Although theoretically, all chemical constituents of a plant are potentially valuable to a taxonomist, in practice some kinds of molecules are more useful than others. Thus we can use directly visible chemical constituents such as crystals, raphides, or starch grains occurring in different plants as chemical characters.