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Basics in Classification

The art of identifying distinction among organisms and placing them into groups that reflect their most significant features and relationship is called biological classification. The purpose of biological classification is to organize the vast number of known plants and animals into categories that could be named, remembered and studied. As a result, the study of one organism of a group gives us the idea about the rest of the members of that particular group. Scientists who study and contribute to the classification of organisms are known as systematics or taxonomists, and their subject is called systematics (Gk, systema: order or sequence) or taxonomy (GK. Taxis: arrangement; nomos; law).

Taxonomic knowledge about the organisms is based on their form and structure (morphology), remnant of the past organisms (fossils) and ecological relationships. This knowledge gained through taxonomy is assembled for future use not only for the biologists but also for others working in the field or medicine, agriculture and forestry or industry and so on. In order to understand the living world, especially its diversity, it is essential to make an inventory of organisms with correct identification and names. It further facilitates classification of organisms based on their similarities or evolutionary relationships (phylogeny). Moreover, the biologists considerably depend on taxonomic studies of fossils for drawing evolutionary relationships among the organisms. You might recall here the impact of taxonomy on different aspects of biology in section 'Scope of Biology”.

Carolus Linnaeus the Swedish naturalist in 1758 postulated the “Two kingdom system of classification”. In this system of classification he divided all the living organisms into two kingdoms Plantae and Animalia. It is used till now. But his classification was insufficient to differentiate some organisms. In order to suggest a better system of classification R. H. Whittaker an American Taxonomists in 1969 postulated “Five kingdom system of classification”. He divided all the living organisms into five kingdoms as Monera, Protista, Fungi, Plantae and Animalia.



Earlier plants were named differently in different regions of the world in their own languages. But these common or local names of the plant have their own weaknesses most important of which are:

They may be quite indefinite, e.g. Pansy has fifty different names in English alone.

They are restricted to the people of one language or even one section of a country. For example, the common names of a weed like Argemone in Hindi are as variable as 'Firangi', 'Dhatina', 'Pila Dathma', 'Sial Kanta', 'Katela', 'Ujar Kanta', Bharband', 'Kandhari', 'Satyanasi Bute', etc. These names are known only to a few people and are therefore, of very restricted use. They are comparable to nicknames of people, which are used only by some of their acquaintances.

They are often misleading and the same name may be applied to entirely different organisms in different parts of the world. For instance, the name 'corn' may mean wheat, maize or any miscellaneous cereal crop.

They are not regulated by any constituted authority.

Because of these problems, common names give a great deal of trouble to a plant collector. As a result a system of binomial nomenclature was suggested by Linnaeus. According to it, a scientific name consists of two parts - the first part is the generic name and the second is the specific name. The generic name is always followed by the specific name. The generic name is a noun and the specific name is an adjective indicating which of the several members of the genus has been considered. Binomials are frequently descriptive of the plants and are usually derived from Greek or Latin. Thus the scientific name of a domestic cat is Felis domestica, of tiger is Felis tigris and that of orange is Citrus reticulate. Such names also give an idea that different species are related to each other. Thus, the scientific name of cat, tiger and lion (Felis leo) clearly indicate that these three species are related to each other.

It is not necessary to always quote scientific names in everyday conversation, but when, one wishes to write the results of a certain experiments on certain organisms or wants to discuss with some other biologists in different parts of the world one has to be specific about the scientific name of the organisms so that it does not cause any misunderstanding.


Need for Classification
There are more than a million kinds of animals and a little less than a million kinds of plants known to biologists. So it is not possible for any one person to study them all. However, if they are grouped in some convenient way, the study would become much easier because the characters of a particular group would apply to all the individuals of that group. Without a suitable method of classification, the study of organisms would be very difficult, as to find out a book from unclassified books in a library. Taxonomy is the branch of biology which deals with the identification, nomenclature of the organisms and their classification in different groups according to their resemblances and differences mainly in their morphological characteristics. The object of taxonomy is not only mere arrangement in some convenient groups but also to give us an idea about their phylogenetic relationships, i.e. the sequence of their origin and evolution from simple, earlier and more primitive types to more complex, more recent and more advanced types in different periods of the earth.

Taxonomic Hierarchy

Hierarchical classification is a system in which individuals are grouped into an ascending series of successively large and broader categories, so that lower groups are always subordinate to and included in those that are higher in the hierarchy. Let us discuss the various categories in the hierarchy. Species is the fundamental unit of classification that can be defined as a group of similar individuals which are capable of interbreeding among themselves. The next higher category is genus (pl. genera) in which a number of different species having certain common basic characters are grouped together. A genus may, therefore, be defined as a collection of closely related species. Various species are grouped together under Genera. Genera are grouped together into families, families into orders and orders into classes. Classes are further divided into bigger categories called divisions or phyla. Phyla are put under the highest category such as Plant or Animal Kingdom.


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