TANONOMIC CATEGORIES

Taxonomic Category is a unit of grouping of any level used in taxonomy or classification of organisms. Usually there are seven obligate and few intermediate categories used in taxonomy.

Hierarchy of categories

It is a system in which members of a type are organized in rank on above the other. Hierarchy of categories or taxonomic hierarchy is the system of arrangement of taxonomic categories in a descending order depending upon their relative dimensions.

It was introduced by Linnaeus and is therefore also called Linnaean hierarchy or taxonomic hierarchy. Linnaeus proposed five categories- class, order, genus, species, and variety. The latter worker deleted the category of variety and added the categories of kingdom, phylum/division, and family

 The taxonomic categories which are always used in hierarchical classification of organisms are called obligate categories. They are seven in number. Obligate categories in descending order are Kingdom, phylum/division, class, order, family, genus and species.

Taxonomic categories introduced in between the obligate categories for accommodating characteristic of certain groups with more precise are called intermediate categories. They are designated by using prefix super or sub to the obligate category.

A new category of tribe has also been raised in between genus and family.

Species (John ray)

It is the lowest or basic taxonomic category which consists of one or more natural population of individuals that resemble one another more closely, interbreed freely, have a distinct genetic set up and reproductively isolated. E.g.- Panthera leo (lion), Mangifera indica (mango), etc.

In organisms lacking sexual reproduction the morphological, anatomical, physiological, cytological and biochemical similarities are taken into consideration.

Some species cannot be divided into race, variety and sub-species. They are called as monotypic species.

Others are polytypic having two or more race, variety and sub-species.

Sub-species/race used commonly by zoologist.

Varieties are used commonly by botanist.

Race is nearly permanent breed within species which is considered equivalent or subordinate to sub-species.

Genus (John ray)

It is the first higher category above the level of species. A genus may have one to several related species.

Genus having single species is called Monotypic and Genus having two or more species is called polytypic.

All the species of a genus have a number of common characters called correlated characters.

E.g.- genus Panthera is polytypic. I has species of Panthera lio(Lion), Panther tigris (Tiger), Panthera onca (Jaguar), Panthera pardus (Leopard).

Family (John ray)

It is category of higher rank than that of genus and is formed of one to numerous related genera/genus which are more similar to one another.

E.g.- family canidia have genera like Canis, Vulpus,Lycoan and Dusicyan.

There is some difference in the suffix used in families. A plant family ends with suffix-aeae and sub-family in oideae. An animal ends with suffix-idea, a subfamily-inae, a tribe- ini while superfamily has the suffix of oidea.

Order (Linnaeus)

It is a taxonomic category having one or more related families that possess some similar correlated characters which are lesser in number as compared to correlated characters or genera of a family.

E.g.- Order Carnivora have families like canidae (dog, wolf, fox), felidae (cat,leopaed, tiger, lion), ursidae (bear) and hyaenidae (hyaena).

Class (Linnaeus)

Class is a major category made of one and more related orders that possess certain similar correlated characters.

E.g.- Ambhibia, aves (birds), Mammalia, etc.

Phylum/Division (Cuvier, Eichler)

It is a taxonomic category higher than class and lower than kingdom in rank. A phylum/division consists of one to several related classes having a few similar correlated characters.

E.g.- porifera, annelid, cnidaeia, chordate, etc.

Kingdom

It is the highest taxonomic category where all the organisms included in it share a set of distinguishing characters.

R.H. Whittaker has recognized five kingdoms of organisms- monera, protista, fungi, plantae (metaphyta) and animalia(metazoan).

It is observed that the number of common or correlated characters is maximum in lower rank categories. The number progressively decreases with the rise in the rank of category.

Therefore, Higher the category , greater is the difficulty in evaluating relationship of its components to other taxa of the same level.

Advantage of hierarchical system of classification

1.      It gives information about the relationship of an organism with others.

2.      It helps in quick identification of a taxon.

3.      All the major traits present in an organism can be studied by noting the trait of various categories in which the organism is classified.

4.      It reduces the volume of traits by non-repetition of correlated traits of a high rank category in the lower rank category.

TAXON

Taxon is a grouping of organisms of any level in hierarchical classification which is based on some common characteristics.