Different systems of classification proposed from time to time have undergone several changes from artificial system to phylogenetic system. Earlier the system of classification was based on one or a few superficial resemblences. For example, animals were classified as aquatic (water dwellers), terrestrial (land dwellers) and aerial (air dwellers). Similarly, plants were classified as herbs, shrubs and trees on the basis of their habit. These systems are artificial. These systems were then followed by natural system which were based on a number of structural and morphological taxonomic characters. Now a days, the organisms are classified on the basis of their evolutionary interrelationship. Such classification are phylogenetic.
