A. AIM OF TAXONOMY:
Plant taxonomy aims to the following
three main headings – Identification, nomenclature and classification.
1.
Identification:- Identification is one of the aims of taxonomy.
Identification of a taxon is a pre-requisite for any study based on it. It is
the determination of a taxon based on overall similarities and differences with
other taxa. Identification is generally done by comparing the representative
specimen of a given taxon with the help of key description, illustrations, etc.
sometimes the specimen may not be resembled or compare with the existing
pre-determined specimen. In such case, it is considered to be new to the plant
science.
2.
Nomenclature:- Once the taxon has been identified, it is necessary to give
it a scientific name. Thus, nomenclature is the naming of a taxon correctly. It
is a precise and universal system of rules used by all botanist of the world
for naming newly discovered plants.
3.
Classification:- Because of the enormously high number of plant species, it
is impossible for anyone to study all the plants individually. To overcome this
problem, the plants can be placed into small or large groups based on their
similarities and their differences, and arranged them under sequential
categories as per the rules.
Classification is thus the
arrangement of an organism in a series of groups or categories depending on
their natural relationship and finally establishing the identity of each
individual.
B. OBJECTIVES
OF TAXONOMY:
The study of plant taxonomy
fulfils the following four main objectives –
1. The first objective is to know
the various kinds of plants on earth with their names, affinities, geological
distribution, habits and their economic importance. It gives an accumulated
information and scientific knowledge of the plant resources.
2. The second objective of plant
taxonomy is to have reference system for plants, where the taxonomists can work
with named entities like species, genus and family.
3. The third objective is to
demonstrate manifold diversities of plant kingdom and their relation to the
evolution of plants. A systematic reconstruction of plant kingdom can be made
only after the complete knowledge of the individual plant. After making the
inventory of the components of plant kingdom, the different facts of
evolutionary knowledge with an accurate phylogenetic scheme can be obtained.
4. The fourth objective is to
ascertain nomenclature. To every name a binomial name is given. For example –
the binomial name of Pea is Pisum sativum. The first name refers to
its genus and the second to its species.
C. PRINCIPLES OF
TAXONOMY:
Taxonomy is one of the oldest
sciences and was practiced by people from ancient India, China, Greece, France,
Germany, UK and other countries. In earlier days taxonomy was mainly aimed at
some convenient methods of classification and communication. This involved
certain principles such as the case of classification, medicinal and other uses
of plants and a set of easily observable characters. Classification of this
type is purely “artificial”.
By the end of 19th
century, attempts to classify plants gradually shifted from artificial to
natural or phylogenetic ones. Thus with the shifting of functions, there has
been a change in principles also. It can be said that the principles of
taxonomy are concerned primarily with the criteria employed in classification.
Cronquist (1968), however
formulated certain basic principles for taxonomy, which are as follows –
1. Taxa are properly established
on the basis of multiple correlations of characters.
2. Taxonomic importance of a
character is determined by how well it correlates with the other characters.
This means that taxonomic importance of a character is determined a posteriori rather than priori.
3. An important feature of
taxonomy is its predictive value.
The first two principles state
the importance of correlation of characters. This is probably the most
important principle of taxonomy. It implies that no characters of a taxon
should be considered singly for the establishment of its relationship with
other taxa but it should always be considered along with other character.
Secondly, the characters chosen
should exhibit maximum correlation with other character. The importance of
characters depends upon the degree of correlation. Anomalous characters are not
taken as granted and are considered as not taxonomically important.
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