Taxonomic Hierarchy of Living Organisms: Unit of Classification



  • Taxonomic Hierarchy of Living Organisms
  1. Species
  2. Genus
  3. Family
  4. Order
  5. Class
  6. Phylum
  7. Kingdom

Taxonomic Categories

[ICSE 9]

GENUS: Similar species constitute the next higher category, called genus (plural: genera). Let us take an example. We have crows around our homes. The hill crow (also called the jungle crow) is different from the crow found on the plains (the house crow) in many features-size, colour, beak, etc. The hill crow and the house crow are two different species. They cannot interbreed; yet they are crows, easily made out from other birds. These two kinds of crows belong to the same genus Corvus. 

FAMILY: A group of genera with certain common characteristics form a family. Take an example. Lion (Panthera leo) and tiger (Panthera tigris) are different species, but they belong to the same genus. This genus (Panthera) and another genus (Pelis) which includes the domestic cat, also share some common characteristics. Therefore, there is the larger cat-family (Felidae) which includes the genus of lion and tiger, and the genus of the domestic cat. 

ORDER: A group of related families makes an order. For example, the cat family Felidae (lions, tigers, and cats) and the dog family Canidae (dogs, foxes, jackals, etc.) possess some common features, and so they make an order. In the example cited here, the order is "Carnivora": 

CLASS: Related orders make a class. For example, the orders of different animals like those of dogs, cats, bats, whales, monkeys, and even humans, etc., have some common features such as hairy skin and milk-glands. The particular class of the animals mentioned here is "Mammalia''. 

PHYLUM: A phylum is the largest division in the classification of plants and animals. Related classes constitute a phylum. For example, the classes of different animals like mammals, birds, reptiles, frogs, fishes, etc., together constitute the phylum Chordata which has a notochord or a backbone. 

KINGDOM: The kingdom is the largest division of living beings.

Taxonomic Categories

[CBSE 11]


Taxonomic studies consider a group of individual organisms with fundamental similarities as a species. One should be able to distinguish one species from the other closely related species based on the distinct morphological differences. Let us consider Mangifera indica, Solanum tuberosum (potato) and Panthera leo (lion). All the three names, indica, tuberosum and leo, represent the specific epithets, while the first words Mangifera, Solanum and Panthera are genera and represents another higher level of taxon or category. Each genus may have one or more than one specific epithets representing different organisms, but having morphological similarities. For example, Panthera has another specific epithet called tigris and Solanum includes species like nigrum and melongena. Human beings belong to the species sapiens, which is grouped in the genus Homo. The scientific name thus, for human being, is written as Homo sapiens.


Genus comprises a group of related species which has more characters
in common in comparison to species of other genera. We can say that
genera are aggregates of closely related species. For example, potato and
brinjal are two different species, but both belong to the genus Solanum.
Lion (Panthera leo), leopard (P. pardus), and tiger (P. Tigris) with several
common features are all species of the genus Panthera. This genus differs
from another genus Felis which includes cats. 


The next category, Family, has a group of related genera with still less number of similarities as compared to genus and species. Families are characterised on the basis of both vegetative and reproductive features of plant species. Among plants, for example, three different genera Solanum, Petunia and Datura are placed in the family Solanaceae. Among animals for example, genus Panthera, comprising lion, tiger, leopard is put along with genus, Felis (cats) in the family Felidae. Similarly, if you observe the features of a cat and a dog, you will find some similarities and some differences as well. They are separated into two different families – Felidae
and Canidae, respectively. 


You have seen earlier that categories like species, genus, and families are based on a number of similar characters. Generally, order and other higher taxonomic categories are identified based on the aggregates of characters. Order, being a higher category, is the assemblage of families which exhibit a few similar characters. The similar characters are less in number as compared to different genera included in a family. Plant families like Convolvulaceae, Solanaceae are included in the order Polymoniales mainly based on the floral characters. The animal order, Carnivora, includes families like Felidae and Canidae.


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Video Tutorials

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Series 2 | Biology Diversity in Living World part 8 (Taxa, taxanomy, Hierarchical) CBSE class 11 XI

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Biology Diversity in Living World part 8 (Taxa, taxanomy, Hierarchical) CBSE class 11 XI [00:14:07]

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