Species : Species is the principal natural taxonamic unit, ranking below a genus and denoted by latin binomial (considered as the basic) unit of classification that can interbreed under natural candition to produce fertile offspring. It was thought to be an indivisible, stable and static unit. However in the modern taxonomy, sub-division of species such as sub-species, varities and population are seen and give more importance.
Genus : Genus is a taxonomic rank or category larger than species used in the biological classification of living and fossil organisms. Genus is a group of species bearing close resemblance to one another in their morphological characters but they do not interbreed, e.g. Tiger, Leoard, Lion all three belong to same genus panthera. They have common characters yet are different from each other because their genus is same but species is different . Another example is genus Solanum. Brinjal and potato both belong to this genus.
Family : It is one of the major hierarchical taxonomic rank. A family represents a group of closely related genera. e.g. genera like Hibiscus, Gossypium, Sida, Bombox are included in same family Malvaceae. Cat also belongs to family of leopards, tigers and lions, family Felidae but dog belongs to different family Canidae.
Cahort / Order : It is taxonomic rank used in the classification of organisms and recognised by nomenclature codes. An order is a group of closely families showing definite affinities. Order this is a step above family in taxonomic hoerarchy. Members belonging to same order but different families may show very few dis similarities. e.g. family - Papavaraceae, Brassicaceae, Capparidance, etc with parietal plancentation are grouped in order Parietales. Families of dogs and cats though are different, they belong to same order Carnivora.
Calss : The calss is the distinct taxonomic rank of biological classification having its own distinctive name. A group of higher taxonomic rank than order. Class is the assemblage of closely allied orders. Orders Carnivora and order Primates belong to class Mammalia. This mankeys, gorillas, gibbons (Primats) and dogs, cats, tigers (Carnivora) belong to same class.
Division / Phylom : The division is a category composed of related classes e.g. division. Angiospermae includes two classes - Dicotyledonae and Monocotyledons (In animal classification division is a sub-unit of Category / Phylum).
Sub-kingdom : Different divisions having some similarities from sub-kingdom. e.g. The division Angiospermae and Gymnospermae will the sub-kingdom Phanerogams or Spermatophyta.
Kingdom : It is the highest taxonomic category composed of different sub- kingdoms. e.g. sub-kingdom Phanerogams and Cryptogams from the Plant kingdom or Plantar which includes all the plants while all animals are included in kindom Animalia.
The taxonomic Categories we have considered so far are broad categories. Scientists have added sub-categories to these in order to place organisms in more scientific manner. You will observe that as we go higher in taxonomical ladder, number of common characters go on decreasing.
If we are comparing two organisms that are related to each other only at division or phylum level, their classification may become difficult.
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