Plants and animals are classified in a hierarchical structure into ranks or categories, based on observable characters. Every category is referred to as a unit of classification called a taxon. Since each category is a part of the taxonomic arrangement, it is known as a taxonomic category and all categories together constitute the taxonomic hierarchy. Organisms are classified into common categories such as kingdom, phylum or division, class, order, family, genus and species.
Species is a group of organisms with fundamental similarities. One species is distinguished from other closely related species based on morphological characters. For example, the different varieties of roses belong to one species. Genus consists of a group of related species that exhibit similar characteristics in comparison to species of other genera. For example, the banyan and peepal trees have certain similarities and belong to the genus Ficus. Family consists of a group of related genera with fewer similarities as compared to genus and species. For example, the lion, the tiger, the leopard and the cat belong to the family Felidae while dog belong to the family Canidae. Order is a collection of related families. For example, families like Felidae and Canidae are included in the order Carnivora. Class consists of related orders. Order Primata includes the monkey, the gorilla and the gibbon, while order Carnivora includes animals like the tiger, the cat and the dog.
Although these two orders are different, they are classified under the class Mammalia. Phylum or division is the next category. Animals like fishes, amphibians, reptiles, birds and mammals have common features like the presence of notochord and a dorsal hollow neural system and are thus categorised as phylum Chordata. Kingdom is the highest taxonomic category, where all the animals are put under Kingdom Animalia and all plants under Plantae.