(Taxa – = arrangement, -nomos= law)
- The process of classification into different taxa is called taxonomy.
- Term taxonomy was first introduced by A.P. de Candolle (Swiss Botanist).
- Modern taxonomy takes an account of the internal and external structures along with the structure of cell, development process & ecological information of organisms.
- Characterization, Identification, Classification & Nomenclature are the processes that are basic stages to taxonomy.
Types of taxonomy:
- Alpha taxonomy: In this stage species are identified and characterized on the basis of gross morphological features.
- Beta taxonomy: In this stage species are arranged from lower to higher categories, i.e., hierarchic system of classification.
- Gamma taxonomy: In this stage intraspecific differences and evolutionary history are studied.
Taxonomical studies of all known organisms have led to the development of common categories such as kingdom, phylum or division (for plants), class, order, family, genus and species. All organisms, including those in the plant and animal kingdoms have species as the lowest category. The basic requirement is the knowledge of characters of an individual or group of organisms. This helps in identifying similarities and dissimilarities among the individuals of the same kind of organisms as well as of other kinds of organisms.
- 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.
- 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.
- 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.
- They are separated into two different families – Felidae and Canidae, respectively
- It is a group of related families.
- 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.
- This category includes related orders. For example, order Primata comprising monkey, gorilla and gibbon is placed in class Mammalia along with order Carnivora that includes animals.
- Classes comprising animals like fishes, amphibians, reptiles, birds along with mammals constitute the next higher category called Phylum.
- All these, based on the common features like presence of notochord and dorsal hollow neural system, are included in phylum Chordata.
- In case of plants, classes with a few similar characters are assigned to a higher category called Division.
- 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.
- The taxonomic categories from species to kingdom have been shown in ascending order starting with species in Figure