Taxonomy

Taxonomy

Biology is an important branch of science dealing with the study of life. It is difficult to define life. But it is easy to discriminate living things from non-living things. On this basis life is defined as a physicochemical entity exhibiting growth, movement, irritability and reproduction. Biology includes two branches, namely Botany and Zoology. Botany deals with the study of plants and Zoology deals with the study of animals.

The art of identifying distinctions among organisms and placing them into groups that reflect their most significant features and relationship is called biological classification. Scientists who study and contribute to the classification of organisms are known as taxonomists, and their subject is called taxonomy (Gk. Taxis = arrangement nomos = law).

The taxonomic hierarchy

It is the sequence of arrangement of taxonomic categories in a descending order during the classification of an organism. Hierarchy was first given by Linnaeus who used only five categories – class, order, genus, species and variety. The last one was discarded and three added so that now there are seven obligate categories. They are : 

Some categories have been added to this list. They are called intermediate categories, e.g., Subkingdom, superphylum or superdivision, subdivision, superclass, subclass, superorder, suborder, superfamily, subfamily, tribe, subspecies, variety etc.

Taxon : The term taxon is used to represent any unit of classification. The unit (i.e., taxon) may be large (e.g., Plant Kingdom) or small (e.g., Algae, Fungi, or a single species).

Category : Various sub-divisions of plants kingdom such as division, class, order, family, etc., are referred to as categories. In the hierarchy of categories kingdom is the highest and species is the lowest category. The following is hierarchical series :

(1) Kingdom : It is the highest category in biological classification. e.g., all plants are include in plant kingdom.

(2) Division : It is a major group in the Linnaean hierarchy used in the classification of plants (equivalent to phylum in animal classification). It is a taxonomic category between kingdom and class. The subcategory of division is subdivision. The suffix of division is – ophyta.

(3) Class : A division is divided into classes. It is a taxonomic category between the division and order. Its suffix is – ae. The subcategories of class are subclass and series. In the class contain organism least similar to one another.

(4) Order : A class includes one or more orders. It is a taxonomic category between the class and family. Its suffix is – ales. The subcategory of order is suborder.

(5) Family : An order is divided into one or more families. It is the taxonomic category between the order and the genus. Its suffix is – aceae. The subcategories of family are subfamily, tribe and subtribe.

(6) Genus : The plural of genus is genera. A family includes one or more genera. The generic name is important and printed in Italics (If hand written, it is underlined). The subcategories of genus are subgenus, section and subsection.

(7) Species : It is the smallest rank of taxonomic classification. The first letter of the species is denoted with small letter. The species is printed in Italics (It is underlined if hand written). A genus may include one or more species. The subcategories of species are subspecies or varieties, subvarieties, form and subform.