Systematics : Taxonomy, Taxonomic Hierarchy and Binomial nomenclature
Systematics : "Systematics is the scientific study of similarities and differences among different kinds of organisms and it also includes their identification nomenclature and classification.
Taxonomy : It is the branch of biology which deals with the collection, identification, nomenclature, description and classification of plants and animals.
Objectives of Systematics/Taxonomy:
i) To know various kinds of plants on the earth with their names, affinities, geographical distribution, habit, characteristics and their economic importance.
ii) To have a reference system for all organisms with which the scientists can work.
iii) To demonstrate the manifold diversities of organisms and their phylogenetic (evolutionary) relationship.
iv) To ascertain nomenclature i.e. scientific name for every organism.
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Classification :
It is the arrangement of organisms of groups of organisms in distinct categories in accordance with a particular and well established plan.
The classification is based on similarities and dissimilarities among the organisms. The term taxonomy was coined by A.P. de Candolle (1813).
Needs of classification :
There is a large number of living organisms found on earth. All these organisms show variations in their shape, size, structure, habit, habitat, nutrition, etc. It is very difficult to remember the characteristics of all the organisms without their proper arrangement. The classification helps to explain unity in diversity of the organisms. It gives specific and scientific names of the organisms which are accepted universally. It reveals the relationships among various groups of organisms. The classification places an organism amongst those which have common characteristics.
The Three Domains of life :
The three domain system was developed by Carl Woese (1990). It is a system for classifying living organisms. From the late 1960's, organisms are being classified according to a Five Kingdom system. Classification systems change as scientists learn more about organisms. Genetic sequencing has given researchers a whole new way of analyzing relationships between organisms. The Three Domain System is primarily based on differences in ribosomal RNA structure of different groups of organisms. Ribosomal RNA is a molecular building block for ribosome. According to this system, organisms are classified into three domains and six kingdoms. The three domains are Archaea, Bacteria and Eukarya.
The domains Archaea and Bacteria include prokaryotic organisms. Three domains include only one kingdom each i.e. Archaebacteria (ancient bactreria) and Eubacteria (true bacteria) respectively. The domain Eukarya includes all eukaryotes. The four kingdoms under this domain are kingdom Protista, Fungi, Plantae and Animalia.
Taxonomic Hierarchy [Gr- Hierarchs = rank]
The main aim of taxonomic study is to assign each organism an appropriate place in a systematic framework of classification. The manner of scientific grouping of different taxonomic categories in a descending order on the basis of their ranks or positions in classification is called taxonomic hierarchy.
In the system of classification the terms like 'taxa' and 'categories' are often used.
1) Taxon :- Taxon is a group of living organisms (Pl. taxa) which is used to represent a concrete unit of classification. The unit or taxon may be large or small. The term taxon was coined by H.J. Lam in 1948 for plants.
2) Category :- A category is a rank or level in the hierarchial classification of organisms. Various taxa are assigned definite categories according to their taxonomic status. In the hierarchy of categories, kingdom is the highest and species is the lowest category.
Example :
Method of classification of China rose and Cobra:
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Units of Classification :
Hierarchy of taxonomic categories
Species :
Species is a smallest and basic unit in the system of classification. All the individual members belonging to a particular species show all similar characters and can breed among themselves to produce similar type of organisms. e.g. All the china rose plants are grouped under a species rosa sinensis, similarly all the potato plants are grouped under a species tuberosum.
Concept of Species :
There are different concepts of species as, morphological concept (Carlous Linnaeus), Biological concept (Charles Darwin) and Modern concept (Ernst Mayr).
According to Linnaeus : A group of organisms which are simillar in their morphological characters is called morphospecies.
According to Darwin : A group of organisms that can interbreed under natural conditions, is called biospecies (True species).
The modern concept according to Ernst Mayr: A group of actually or potentially interbreeding natural population of closely resembling organisms is called species.
Genus : (PI. genera) - It is a group of closely related species, which reemble one another in certain characters, e.g. rosa-sinensis, esculentus, canabinus etc. are different species under the genus Hibiscus. A genus may be either monotypic (having single species) or polytypic genus (having many species).
Family : A family represents a group of closely related genera. The genera like Hibiscus, Malva, Sida, Gossypium, Abutilon, etc. belong to the family Malvaceae.
Order : It is a group of closely related families which resemble in major characters. For example families Malvacear, Tiliaceae, Sterculiacear etc. Belong to the order Malvales. (They show axile placentation in ovary)
Sub-Class : It is assemblage of different orders having some similarities. For example he orders, Malvales, Rananles, Parietales etc. have free petals and hence grouped under the sub-class Polypetalae.
Class : It is a group of related sub-classes. For example the class Dicotyledonae includes sub-classes as Polypetalae and Gamopetalae.
Division : The division is a category composed of related classes. For example, division Angiospermae includes two classes- Dicotyledonae and Monocotyledonane. (In animal classification instead of Division the category Phylum is used ).
Sub Kingdom : Different divisions having some similarities from sub-kingdom. For example the divisions Angiospermae and Gymnospermae will form the sub kingdom Phanerogams or Spermatophyta. (All seed producing plants)
Kingdom : It is the highest taxonomic category composed of different sub kingdoms. For example, sub-Kingdom Phanerogams and Cryptogams, for the Plant kingdom or plantae which includes all the plants while all animals are included in Kingdom Animalia.
Nomenclature [Nomen = name; Calare = to cell]
Any object that becomes known to human intelligence is given a name. Just as all known objects are given names, plants and animals also are identified by their names. The art of naming an object is in fact a science called nomenclature.
The nomenclature has two main purposes:
i) As an aid to communicate and
ii) To indicate relationship.
1. Vernacular Names :
These are the names which are given to organisms in a particular region and language by local people. All plant and animals are known by different common names in different parts if the world. Sometimes, within the same country, people of different states and regions use different common names for single plant. The local or vernacular names are short, familiar and easy to follow. However, these names do not indicate proper relationship and are not universal. For example, in India Ipomoea batatas is recognized by various names like sweet potato (in English); Shakarkand (in hindi); Meetha Alu (in Assamese and Bengali); Kandmul (in Telugu); Ratalu (in Marathi) and Jenasu (in Kannada), etc. It means the local names are different and so, Confusing. A single vernacular name is used for several species. For example, the name "lily" is used to describe many bulbous flowering plants like - water lily, spider lily, etc. Vernacular names may be misleading. For example, starfish, jelly fish, silver fish are not fishes at all. Thus, vernacular names create confusion.