Taxis = arrangement, nomos = law. Taxonomy
All living organisms are classified into various groups based on their characteristics according to the principles of identification, nomenclature and classification. The branch of biology which deals with the study of identification, classification and nomenclature is known as taxonomy.
The arrangement of organism in taxonomic group according to similarities and dis-similarities is known as classification. The purpose of biological classification is to organise the vast number of known organisms into categories that could be named, remembered and studied. There are two types of classification: Empirical Classification and Rational Classification.
In this type, the actual nature or character of plants is not considered. Plants are classified on the basis of their alphabetical order of their name. On the basis of name, plant kingdom can be classified into 26 groups.
In this classification, plants are classified on the basis of their actual character or nature. There are three principle system of classification- artificial, natural and phylogenetic systems.
It is based on one or few external morphological characters of organisms. It is earliest system of classification. Example: Theophrastus classified plants as trees, shrubs and herbs. Aristotle classified animals as enaima and anaima, on the basis of the presence or absence of red coloured blood.
Natural system of classification
It is based on the overall morphological, embryology and anatomical characteristics, which indicate natural relationships among organisms. Example: George Bentham and J. Hooker gave most important natural system of classification of angiosperms, published in ‘Genera Plantarum‘.
Phylogenetic system of classification
This system of classification is based on the evolutionary descent of a group of organisms. In this system, organisms belonging to the same taxa are believed to have common ancestry and may be represented in a family tree called cladogram.
Taxonomical categories is also called Liennean hierarchy or taxonomical hierarchy. It is the classification of organism in a definite sequence of categories in a definite sequence of categories from kingdom to species or from species to kingdom. There are seven categories:
A single organism will be called in different names in different countries. Even in a single country it has several names in different regions, because of different languages. Another point is that some common names are quite misleading like, silver fish, jelly fish, star fish etc. are not true fishes. These problems can be resolved only when all living organisms are identified, classified and given scientific nomenclature.
Binomial system of nomenclature
The binomial system is system of classification developed by Carolus Linnaeus, a swedish naturalist. According to this system, each organism is given only one name consisting of two words. Linnaeus proposed scientific name of plants in his book “Species plantarum” and name of animals in his book “Systema naturae”.
According to binomial system name of any organism consists of two components or words: Genetic name (name of genus) and Specific epithet (name of specis).
In plant nomenclature tautonyms are not valid i.e. generic name and speific epithet should not be same. But tautonyms are valid in animal nomenclature. eg. Naja naja (Indian cobra) and Rattus rattus (Rat).
First letter of generic name should be in capital letter and first letter of specific epithet should be in small letter.
Scientific name should be derived from latin or greek languages because they are dead languages.
When written with free hand or typed, then generic name and specific epithet should be separately underlined. But during printing name should be in italic to indicate their latin origin.
Name of the scientist (who proposed nomenclature) should be written in short after the species name. But name of scientist should be neither underlined nor written in italics. eg. Mangifera indica Linn.