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Hierarchy of Categories/Groups


The basic unit of classification is the species. All plants which resemble one another in almost all respects and which may be considered to be the descendents of common parents are said to belong the same species.


Example : all the tomato plants of the world form one species. They all reproduce their kind and the offspring resemble the parents in all respects.


Members of one species cannot breed with members of a different species. The term ‘species’ was first proposed by an English Naturalist, John Ray, in the 17th century. By convention, the names of species should always begin with a small letter.

John Ray

All the species, which are related to each other by some common characteristics, are brought together into a larger group called genus.


Example : Potato (Solanum tuberosum), tomato (ycoperiscum esculentum) and brinjal (Solanum melongena) are three species, which belong to the genus Solanum.


The concept of genus, as it is understood today, was first recognised by Brungels and later by Tournefort. Tournefort’s concept of several genera was adopted by Linnaeus sometimes with, and sometimes without, any modifications. Tournefort is therefore considered the Father of plant genera. By convention, the generic name should always start with a capital letter.



Many related genera are grouped together as a family.
While deciding on a family name, the name of a particular genus is chosen as the basis for the family. Lamium is the type genus for the family Lamiaceae. All the family names, except a few are based upon their respective type genus. The family name is generally suffixed by ‘ceae’.


Example : The two genera Hibiscus and Thespesia. Since they resemble each other in a number of characteristics, they are said to belong to a common family, Malvaceae.



An order includes one or more number of related families. The name of the order generally ends with ‘ales’.


Example : Malvales, Rosales.



A group of related orders form a class.


Division or Phylum

Certain classes together form a division. These divisions are found in the plant kingdom.



Naming Families, Genera and Species

A family may be named after some important genus included in it.

Example : Malvaceae, after the genus Malva.


The family name may be derived from some characteristic features exhibited by the plants belonging to it.

Example : Cruciferae because of the cruciform corolla of its plants.


A genus is generally named either after some famous botanist or some peculiar structure or habit.

Example : Adanosonia (Adanson, a botanist), Bahunia (Bahuin, a botanist), Convolvulus (convolute corolla).


A species name is derived in various ways. A species may be named after its discoverer.

Example : Crotalaria fysonil, or after some eminent botanist, e.g., Oenothera lamarkiana.


The species may refer to the country where it was found originally or to some particular place in a country.

Example : Agave americana, Bombax malabaricum.


It is usual to put the name of the person who described it, either the genus or the species, in an abbreviated form.

Example : Cassia, Linn (Linnaeus), Pithecolobium dulci, Benth (Benthem). This is referred to as author citation.


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