Taxonomy of Angiosperms #Part -I # Principles & Practices# 2 #:Rank of Taxa# 4thSem Honours# TU

           Rank of Taxa:  Hierarchy is the method of arrangement of categories and taxa in an ascending order so that a higher category includes one or more lower category / categories.Whereas,a "taxon" is a group of real organisms recognised as a formal unit at any level of a hierarchic classification; and "category"is the term used to designate the rank.

 e.g. in the Binomial Oryza sativa ; Oryza is the taxon and Genus is the category.

  In a hierarchic classification taxons are arranged according to Linnaean Hierarchy where seven obligatory categories  for classification of animals were:

Kingdom

     Phylum

          Class

               Order

                     Family

                          Genus

                               Species

                                   Variety

In Plant Taxonomy category Phylum was replaced by Division and Cohort may be used in place of Order but variety was not initially used.

     Later , categories were further splitted and new categories were introduced :

  "Tribe " in between Family and Genus and many  categories were created by adding prefixe Sub- :

  e.g. Basic category is Class

          New category is Sub-Class.

So, the hierarchy turns as:

Kingdom

    Division

       Subdivision

           Class

              Subclass

                  Order

                      Suborder

                           Family

                               Subfamily

                                   Tribe

                                      Subtribe

                                          Genus

                                              Species

Further taxonomists are authorised to form additional categories like

(i) section, series in between genus and species,

(ii) variety and form below species.

     A variety is an intraspecific category and during nomenclature it's rank is mentioned with binomial by adding var. in between them.

e.g. Vitex trifolia var. simplicifolia Cham.

Ending of rank names:

Division                 -phyta

Subdivision          -icae

Class                     -opsida

Subclass.             -idae

Order.                   -ales

Suborder.            -ineae

Family.                -aceae

Subfamily.          -oidea

Tribe.                   -eae

 Review

(1) Define Hierarchy.

(2)What are Taxon and Category?

(3) Distinguish between Taxon and Category.

(4) Write a brief note on Rank of Taxa.