In biological classification, Taxonomic hierarchy is the process of arranging various organisms into successive levels of the biological classification from kingdom to species and vice versa.
Each level of this hierarchy is called a Taxonomic rank.
A given rank subsumes under it less general categories, that is, more specific descriptions of life forms. Above it, each rank is classified within more general categories of organisms and groups of organisms related to each other through inheritance of traits or features from common ancestors.
Taxonomic ranks are:
1. Domain
2. Kingdom
3. Phylum(zoology) OR Division(Botany)
4. Class
5. Order
6. Family
7. Genus
8. Species
Index
History
The number of species that are known and described ranges between 1.7-1.8 million. This refers to biodiversity or the number and types of organisms present on earth.
We should remember here that as we explore new areas, and even old ones, new organisms are continuously being identified.
Moreover, we know all these plants and animals by local names. Thus arises a need for a standard naming convention and a standard classification of all these organisms.
It is believed that Greek philosopher Aristotle firslty classified different animals based on the habitat, characteristics, etc
Then, Carl Linnaeus, Swedish botanist, zoologist, taxonomist, and physician came up with the current taxonomic hierarchy in the 18th century. Linnaeus established a naming system called binomial nomenclature which is used even today. He is known as the “Father of modern taxonomy“.
In binomial nomenclature, each name has two components – the Generic name and the specific epithet.
Let us first see a bit about this nomenclature and then let us understand the taxonomic hierarchy
Nomenclature Rules
- Biological names are generally in Latin and written in italics. They are Latinised or derived from Latin irrespective of their origin.
- The first word in a biological name represents the genus while the second component denotes the specific epithet (distinguishes the species from others in the same genus).
- Both the words in a biological name, when handwritten, are separately underlined or printed in italics to indicate their Latin origin.
- The first word denoting the genus starts with a capital letter while the specific epithet starts with a small letter.
Example: Mangifera indica (Mango).
The name of the author appears after the specific epithet, i.e., at the end of the biological name, and is written in an abbreviated form
Taxonomy
Taxa is any unit used in the science of biological classification, based on characteristics, all living organisms can be classified into different taxa. This process of classification is Taxonomy.
Characterization, identification, classification, and nomenclature are the processes that are basic to taxonomy.
Taxonomic Categories or Ranks
Species
A group of individual organisms with fundamental similarities. We should be able to distinguish one species from the other closely related species based on the distinct morphological differences. Around 8.7 million different species is known to exist on the planet.
Example: Panthera pardus (Leopard), Panthera leo (Lion)
Here; pardus & leo are the species name.
Genus
Genus comprises a group of related species that has more characters in common in comparison to species of other genera.
Example: Lion and Leopard are two different species but both belong to the same genus Panthera.
Family
The family has a group of related genera with still fewer umber of similarities as compared to genus and species. Families are characterized based on both vegetative and reproductive features of plant species.
Example: Leopard (Panthera genus) and Bay Cat (Catopuma genus) belongs to Felidae family.
Order
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 that exhibit a few similar characters. The similar characters are less in number as compared to different genera included in a family.
Example: The animal order, Carnivora, includes families like Felidae and Canidae.
Class
The class is a distinct rank of biological classification having its distinctive name. The class was the most general rank in the taxonomic hierarchy until phylum was not introduced.
For Example Order Proboscidea (elephants), Order Primates (primates) and Order Pinnipedia (seals and walruses) are placed in the class Mammalia.
Phylum
Different classed then constitute a Phylum.
The classes of the Phylum Chordata are the Amphibia, the Reptilia, the Fish, the Birds, and the Mammalia.
Kingdom
A kingdom is the highest level of classification. There are 5 kingdoms in which the living organisms are classified, namely, Animalia, Plantae, Fungi, Protista, and Chromista.
All animals belonging to various phyla are assigned to the highest category called Kingdom Animalia in the classification system of animals.
The Kingdom Plantae, on the other hand, is distinct and comprises all plants from various divisions. Henceforth, we will refer to these two groups as animal and plant kingdoms.
Domain
A domain is the highest taxonomic rank of organisms in the three-domain system of taxonomy introduced by Carl Woese in 1990
According to this system, the tree of life consists of three domains namely
1. Archaea
2. Bacteria
3. Eukarya
The first two are all prokaryotic microorganisms, or mostly single-celled organisms whose cells have no nucleus. All life that has a cell nucleus and eukaryotic membrane-bound organelles is included in Eukarya.
Application
Taxonomic hierarchy is used for the classification of an organism, and the information gathered is also stored along with the specimens.
These, along with their descriptions become a storehouse or repository for future use.
Questions
Question 1. What is the scientific name of Mango, Apple, Rice, Papaya?
Answer. Mango – Magnifera indica
Apple – Malus domestica
Rice – Oryza sativa
Papaya – Carica papaya
Question 2. Give the correct sequence of taxonomical categories.
Answer. Domain > Kingdom > Phylum(zoology) OR Division(Botany) > Class > Order > Family > Genus > Species
FAQs
We give them names under Binomial Nomenclature because one animal can have different names by which it is recognized worldwide. So, by this way we give them a specific name as well, we are also able to relate them to tracking back their ancestors, keeping an organized document that is easy to refer to.
While writing or typing any scientific name there are some come things such as:
1. Always start Genus name with capital and species name with a lowercase letter.
2. Both must be written separately.
The difference stands that while writing by hand both of them must be separately underlined, but while typing it must be made into Italics.
Phylum or division is the next classification to class.
The difference stands Phylum is used in classifying animals(zoology) & Division is used in classifying plants(Botany).
The name of the author appears after the specific epithet, i.e., at the end of the biological name, and is written in an abbreviated form, e.g., Mangifera indica Linn. It indicates that this species was first described by Linnaeus.
That’s all about Taxonomic Hierarchy.
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