Taxonomy and Systematics: Definition, Differences, Hierarchy & Nomenclature
Taxonomy & Systematics
1. Diversity of Living Organisms
There are differences among organisms in:
- Habit
- Habitat
- Structure
- Function
The estimated number of species is about 1.7 million according to Robert May.
TAXONOMY & SYSTEMATICS
1. Taxonomy
Term
The term Taxonomy was coined by A. P. de Candolle.
Definition
Taxonomy is the study of the principles and procedures of classification.
Components of Taxonomy
- Characterisation
- Identification
- Nomenclature
- Classification
2. Systematics
Term
The term Systematics was coined by C. Linnaeus.
Definition
Systematics is the study of the diversity of living organisms along with their comparative and phylogenetic relationships.
Components of Systematics
- Characterisation
- Identification
- Nomenclature
- Classification
- Phylogeny
Important Relationship
Systematics = Taxonomy + Phylogeny
Identification
Identification is the proper placement of an organism into any accepted system of classification.
Nomenclature
Nomenclature is the system of naming organisms.
Classification
Classification is the arrangement of organisms into different groups and subgroups.
Taxonomic Hierarchy
Taxonomic hierarchy is the arrangement of different groups or categories/ranks in an ascending or descending order.
Important Points
- Each rank of taxonomic hierarchy is called a category or taxon.
- Taxon represents categories of different ranks.
- Taxon represents a unit of classification/taxonomic hierarchy.
Linnaean Hierarchy
The first taxonomic hierarchy was proposed by C. Linnaeus.
It included only five categories:
Class → Order → Genus → Species → Variety
Modern Taxonomic Hierarchy
Modern hierarchy includes 7 obligatory categories and several intermediate categories.
Sequence of Obligatory Categories
Kingdom → Division/Phylum → Class → Order → Family → Genus → Species
For plants, the term Division is commonly used, while Phylum is commonly used for animals.
Basic Unit
The basic unit of taxonomic hierarchy is Species.
Important Trend
As we proceed from lower to higher categories:
- The number of individuals gradually increases.
- Common characters gradually decrease.
Terms Associated with Taxonomic Categories
- Division — Eichler
- Phylum — Cuvier
- Class and Order — Linnaeus
- Family and Species — John Ray
- Genus — Tournefort
- Concept of Genus — associated with Tournefort
Species
Species is the basic unit of taxonomic hierarchy.
Only the species represents an actual biological unit; the other higher categories of taxonomic hierarchy are considered hypothetical/abstract groupings.
Specific Epithet
The specific epithet is the second part of a scientific name in binomial nomenclature.
A biological name does not represent an organism by the specific epithet alone. The specific epithet must be associated with the generic name.
Important Point
Each genus may have one or more specific epithets.
Example: Solanum
Different species of the genus Solanum include:
- Solanum tuberosum — Potato
- Solanum melongena — Brinjal
- Solanum nigrum — Black nightshade
Example: Panthera
- Panthera leo — Lion
- Panthera tigris — Tiger
- Panthera pardus — Leopard
Genus
A genus is an aggregation of closely related species.
Family
A family is a group of related genera.
Genera belonging to the same family share fewer common characteristics than organisms belonging to the same genus or species.
Example
Family — Solanaceae
Some genera include:
- Solanum
- Datura
- Petunia
Important Point
Families are based on both:
- Vegetative characters
- Reproductive characters
Order
An order is an aggregation of related families with a smaller number of common characters than genera and species.
Important Point
In the notes:
Order is mainly based on floral characters.
Example
Order — Polymoniales
It includes families such as:
- Solanaceae — potato
- Convolvulaceae — sweet potato
Taxonomic Categories — Examples
| Organism | Family | Order | Class | Phylum/Division |
|---|---|---|---|---|
| Human | Hominidae | Primata | Mammalia | Chordata |
| Housefly | Muscidae | Diptera | Insecta | Arthropoda |
| Mango | Anacardiaceae | Sapindales | Dicotyledonae | Angiospermae |
| Cactus | Poaceae | Poales | Monocotyledonae | Angiospermae |
NOMENCLATURE
There are two systems of nomenclature:
- Vernacular name
- Scientific name
Vernacular Name
The common/local name of an organism is called its vernacular name.
Scientific Name
The scientific name is a universally accepted name used for an organism.
Binomial Nomenclature
Binomial nomenclature is the system of naming organisms using two words.
The two words are:
- Generic name
- Specific epithet
Example
Solanum tuberosum
- Solanum → Generic name
- tuberosum → Specific epithet
Important Point
The scientific name consists of two words and is therefore called binomial nomenclature.
Rules of Binomial Nomenclature
- The generic name begins with a capital letter.
- The specific epithet begins with a small letter.
- The complete scientific name is written in italics when printed.
- When handwritten, the generic name and specific epithet are underlined separately.
- Scientific names are generally based on Latin or Latinised words.
Example
Printed: Solanum tuberosum
Handwritten:
Solanum tuberosum — both words underlined separately.
Trinomial Nomenclature
In some cases, a third name is added to indicate a subspecies or other infraspecific category. This is called trinomial nomenclature.
Important Historical Points
The notes also mention important changes in botanical nomenclature:
- ICN — International Code of Nomenclature
- Earlier botanical nomenclature codes have undergone revisions.
- Modern nomenclature follows internationally accepted rules.
Botanical Nomenclature
The International Code of Nomenclature for algae, fungi and plants (ICN) provides internationally accepted rules for naming these organisms.
Quick Revision
Taxonomy → Principles and procedures of classification
Systematics → Taxonomy + phylogenetic relationships
Identification → Proper placement of an organism
Nomenclature → Naming of organisms
Classification → Arrangement into groups and subgroups
Taxon → Unit/category of classification
Species → Basic unit of taxonomy
Genus → Group of closely related species
Family → Group of related genera
Order → Group of related families
Binomial nomenclature → Two-word scientific naming system
Generic name → First word, capitalised
Specific epithet → Second word, lowercase
