Taxonomic Hierarchy Categories were also introduced by Linnaeus. They are also known as Linnaean hierarchy. It is defined as sequence of categories in a decreasing or increasing order from kingdom to species and vice versa. Kingdom is the highest rank followed by division, class, order, family, genus and species. Species is the lowest rank in the Hierarchy. The hierarchy has two categories which are obligate and intermediate. Obligate means they are followed strictly and range from kingdom to species as said above. Intermediate are not followed strictly and they are added in obligate list such as subdivision, super family, super class, suborder, subspecies etc.
1. Species: Group of population which is similar in form, shape and reproductive features so that fertile sibling can be produced. Some siblings can be sterile when a hybrid is produced. A hybrid can be product of female horse & male donkey (Mule). Or male tiger & female lion known as Tigon. Sexual reproduction is present in eukaryotes. Species is followed by subspecies, varieties and races. These categories are inferior as compared to species.
2. Genus: It is defined as group of similar species. But it is not mandatory to have many species. Some genera have only one species known as Monotypic. If there are more than one species it is known as polytypic. For example lion, tiger are quite similar species placed under the genus Panthera.
3. Family: It is defined as collection of similar genera. It can be separated from genera by reproductive and vegetative features. For example, cats and leopard are included in the family felidae.
4. Order: One or more than one similar families constitute order. Family felidae are included in the order Carnivora.
5. Class: One or more than one order makes a class. Class mammalia includes all mammals which are bats, rodents, kangaroos, whales, great apes and man.
6. Phylum: It is a term used for animals while its synonym division is used for plants. It is a collection of similar classes. Phylum chordata of animals has class mammalia along with birds, reptiles and amphibians.
7. Kingdom: The top most taxonomic category. Example all animals are included in Kingdom animalia.The unit in classification that denotes grouping of organism based on features which are observable is known as Taxon.
The different methods used to identify and classify organisms are referred to Taxonomic aids. Identification of organisms is a tedious process. Keys are used for identification referred as Taxonomic key. It includes a long table of statements with alternative features to identify organisms. The features which are related to organism are chosen.
The statement is referred to key. There are separate keys for different taxonomic category. Basically, they are of two types indented and bracketed. The former constitutes range of choices between two or more features. While the later uses contrasting features with each feature having a specific number enclosed in brackets.