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In this article we will discuss about the Meaning and Stages of Chemotaxonomy.
Meaning of Chemotaxonomy:
Chemical systematics is the study of chemical variation in different organisms and their relationships and this approach of taxonomy in which chemical features of plants are used in developing classifications or in solving taxonomic problems is called Chemotaxonomy. Data from chemistry of plant products is termed photochemistry.
The principles, procedures and results of investigations of chemical variation of plant groups can be applied mainly for two purposes:
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I. To provide taxonomic characters which may help in plant classification and may improve the existing systems of plant classification.
II. To have additional knowledge of phylogeny or evolutionary relationships of plants.
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Chemotaxonomy has been used in all the groups of the plant kingdom starting from the simple organisms, such as fungi and bacteria, up to the most highly advanced and specialized groups of angiosperms and at all levels of the hierarchy of classification in plants, starting from the rank of Variety up to the rank of Division.
Chemical characters are particularly of high taxonomic value when they are stable, unambiguous and not easily, if at all, changeable.
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The use of chemical characters in plant classification has a long history. Since the early 1960s, phytochemical characters started to attract the attention of plant taxonomists.
However recently, due to the development of new and powerful analytical techniques and the speed and simplicity of these techniques, it has been possible to screen a large number of individuals in a very limited time and utilize such information in plant taxonomy.
The various data from these studies confirms early ideas that phytochemical characters correlate quite well with other types of characters and should be considered seriously in taxonomy.
However, at the same time, chemotaxonomy should not be considered as more indicative of relationship than other characters such as external morphology, anatomy, cytology, etc. and as a replacement of other taxonomic characters, but at best a major source of new characters and information.
The new ideas and facts that are still being obtained from all other existing sources of taxonomic evidence should not be ignored. The chemical characters are considered more important, only when they show a high degree of correlation with other features.
Stages in Chemotaxonomy:
Hegnauer recognized six chief stages in a phytochemical study, reconciling the need for informed chemical procedure and a project design satisfying formal taxonomic requirements:
(i) Choice of a group, taxonomic survey and sound sampling.
(ii) Choice, mastery and modification of suitable chemical techniques in a pilot survey.
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(iii) Full analysis of all material.
(iv) Interpretation and comparison with data from all other sources.
(v) Adjustment of classification as necessary, and
(vi) Treatment of any evolutionary relationship as indicated by the new data.
