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Systematics
The word systematics is derived from the Latin word 'Systema', meaning order or sequence.
It is the branch of science that deals with the arrangement of diverse organisms in an organised plan according to the distinct/unique features of the organisms; it creates order out of chaos.
Though the words 'systematics', 'classification' and 'taxonomy' are used interchangeably (i.e., as synonyms) some taxonomists relate them to different fields.
According to Simpson, Systematics is the study of diversity of organisms and all their comparative and evolutionary relationships.
According to him, classification is a subtopic of systematics and is defined as the process the organisms are grouped on the basis of their relationships.
- Identification (assigning the organism to a particular group)
- Classification (arrangement of organisms into groups)
- Nomenclature (naming the organisms)
- Taxonomy (framing rules for classification).
Identification
Identification refers to the assigning of an organism to a particular taxonomic group. A study is carried out to recognise the characteristic features of various parts of an organism and these features are compared with those of the already known species, to determine their similarities and differences.
Classification
Classification is the art of identifying distinctions among organisms and placing them into groups that reflect their most significant features and relationships.
The purpose of biological classification is to organise the vast number of known organisms into categories, that could be named, remembered and studied. Biological classification has two functions:
1. To recognise and describe as completely as possible, the basic taxonomic units or species.
2. To devise a way of grouping these units on the basis of their resemblances and relationships.
Advantages of classification
- It makes the study of such a wide variety of organisms easy, systematic/scientificand convenient.
- It allows us to identify organisms and also to recognise those already classified.
- The study of one or a few representatives of every group will give us an idea of the other forms in that group as it is not possible to study each of them individually.
- It helps in understanding the interrelationship among different groups of organisms.
- It gives an idea about the organisms that are not present in one's place/locality. It reflects the evolutionary trends among organisms.
- It enables the scientists to interpret the structures of fossil organisms.
History of classification
1. The first attempt to classify animals is seen in Chandyogya Upanishad, which classified animals into three categories:
(i) Jivaja (viviparous)
(ii) Andaja (oviparous) and
(iii) Udbhija (vegetal origin).
2. Post-vedic literatures like Susruta Samhita (600 BC) classified all 'Substances' into Sthavara (immobile, e.g., plants) and Jangama (mobile, e.g., animals).
3. Greek scholars Hippocrates (460-377 BC) and Aristotle (384-322 BC) classified animals into four major groups, namely insects, birds, fishes and whales.
4. Theophrastus (370-285 BC) grouped the plants into four categories based on their habit, form and texture; they are trees, undershrubs, shrubs and herbs. He described 480 plants in his book Historia Plantarum.
5. Charaka (First century AD) listed the names of over 200 types of animals and 340 plants in his book Charaka Samhita on Indian medicine.
6. Caius Plinius Secundus (23-79 AD) carried on the taxonomic work further and introduced the artificial system of classification; his book Historia Naturalis mentions about 1000 economically important plants; he used the term 'stamen' for the first time.
7. Andrea Caesalpino (1519-1603 AD) described 1520 plant species in sixteen volumes of the book De Plantis libri.
8. John Ray (1627-1705 AD) coined the term species and attempted to distinguish genus from species; he described more than 18,000 plants and animals in his book Historia Generalis Plantarum.
9. Carolus Linnaeus (1707-1728) has described 5900 species of plants in his book Species Plantarum (1753) and 4326 species of animals in Systema Naturae (1758); he classified animals into mammals, birds, amphibians, fishes, insects and worms.
10. Michel Adanson (1727-1806) classified plants and animals using a natural system.
11. A.P. de Condolle (1778-1841) published a new classification of plants in his book Theorie Elementaire de la Botanique (1813).
12. George Bentham (1800-1884) and Dalton Hooker (1817-1911) published their natural system of classification in Genera Plantarum; this system of classification is considered the best for practical purposes and is followed in most of the herbaria.
13. Eichler (1839-87) published a phylogenetic classification in 1883.
14. Engler (1844-1930) and Karl Prantl (1849-1893) also classified plants on the basis of their evolutionary relationships, starting with the simplest flowering plants and ending with plants having complex floral structures.
15. Bessey (1845-1915) classified plants on the basis of evolutionary relationships.
16. Hutchinson (1884-1972) published the phylogenetic classification in his book The Families of Flowering Plants.
17. Armen Takhtajan (1980), published a system of classification in Botanical Review; he wrote 'Taxonomy without phylogeny is like bones without flesh'.
18. Arthus Cronquist (1981) published his classification in 'An Integrated System of Classification of Flowering Plants'.
Classical Systematics and New Systematics
Systematics from the earliest times starting with Plato and Aristotle to the time of Linnaeus, is known as Classical taxonomy.
Systematics of the post-Linnaean period, is known as New or Modern systematics; the term New systematics was proposed by Sir Julian Huxley in 1940.
Classical systematics
- Classical systematics is based only on a few observable morphological and/or anatomical characteristics of the individuals.
- It follows the typological concept of species, which originated in the philosophies of Plato and Aristotle and accepted by Linnaeus.
- According to this concept, the observed diversity in nature can be reduced or generalised to a limited number of types.
- The individuals are merely the expressions of the same type and the variations in the individuals are only imperfect expressions of the type.
- As a result, according to this concept, species is a fixed or static and immutable (unchangeable) entity.
New systematics
• It is also known as population systematics and biosystematics.
• It tries to bring out the evolutionary relationships among organisms.
• This system is based on the study of all types of variations in the species.
According to this system, species are considered dynamic and everchanging/mutable
entities; they form the centre stage of systematics.
• Subspecies and populations have also been given emphasis.
• The morphological definition has changed to biological definition.
•The following are the forms of new systematics:
(i) Morphotaxonomy (ii) Cytotaxonomy, (iii) Chemotaxonomy and (iv) Numerical
Taxonomy.
Nomenclature
Nomenclature refers to the assigning of names to organisms.
Names are based on certain observable/morphological and distinct characteristics as well as the similarities with the already known organisms.
The common names in the local languages are called vernacular names: but it is not possible to identify the organisms universally based on the vernacular names for the following reasons:
1. The vernacular names change with the different languages: e.g., China rose in English, Jaswand in Marathi, Padmacharini in Sanskrit and Gurhal in Hindi.
2. A common name may include more than one type of organisms, e.g., Titlee in Hindi includes moths and butterflies.
3. The common names may be misleading, e.g., Jellyfish and Starfish are not fish at all. So scientists/biologists have established procedures to assign a scientific name to each known organism.
The following are the methods of providing scientific names to the organisms:
Polynomial nomenclature
• This method of naming plants that was in vogue before1750 AD, used to add a series of descriptive words and make the names very long and difficult to remember.
• It can be illustrated with the example of Caryophyllum; the name given to it was Caryophyllum saxatilis, folis graminous, umbellatus corymbis; it means that Caryophyllum grows on rocks, has grass-like leaves and umbellate-corymb arrangement of flowers.
• The system of naming a plant with a string of such Latin words, is called polynomial nomenclature (poly-many; nomen-name).
Binomial nomenclature
Carolus Linnaeus (1758) introdućed this system of naming organisms.
• In this method, every organism is given a scientific name, which has two parts (bi-two; nomen-name); the first is the name of the genus (generic name) and the second is the name of the species (specific epithet), e.g., Mangifera indica (mango) and Homo sapiens (Human being).
Trinomial nomenclature
• In these examples, Mangifera and Homo are generic names, while indica and sapiens are the names of species belonging to Mangifera and Homo respectively.
• Occasionally, three words are used in the scientific name of organisms, especially animals.
• These names include the generic, specific and sub-specific names of organisms,
e.g.. Scientific name of modern man is Homo sapiens sapiens.
Puccinia graminis tritici is a fungus that attacks wheat.
Corvus splendens splendens--Indian crow.
Corvus splendens protegatus-Srilankan crow.
Guidelines for naming of organisms
• The rules of nomenclature are framed and standardised by the International Committee, that includes the following:
1. International Code of Botanical Nomenclature (ICBN) (1961) for plants.
2. International Code of Zoological Nomenclature (ICZN) (1964) for animals. names.
3. International Code of Viral Nomenclature (ICVN) for viruses.
4. International Code of Nomenclature of Cultivated Plants (ICNCP).
• These codes help in avoiding errors, duplication, confusion and ambiguity in scientific
• These codes are established and improved upon at International Botanical and Zoological Congress, held from time-to-time.
Taxonomy
- Simpson has defined taxonomy as the study of principes and procedures of classification.
- The word 'taxonomy' has been derived from the Greek word - taxis meaning arrangement and nomos meaning law.
- The term 'taxonomy' was coined by A.P. de Condole.
Taxonomic knowledge of organisms is based on the following:
- Form and structure (Morphology)
- Cell Structure (Cytology)
- Development processess (Embryloogy)
- Remnants of the past organisms (Fossils)
- Ecological relationships.
Basis processes of Taxonomy
Characterization
- The organisms is described for all its morphological and other character.
Identification
- On the basis of its characterization, it is decided whether it is similar to a known group of taxonomy or not.
Classification
- Based on the similarites in character, it is then placed in a known taxon.
Nomenclature
- Once it is placed in a taxon, its correct name is determined.
- If the organism has not been described before, it is given a new name.
Taxonomic Hierarchy
Species
- The individuals of species also represent a population of that species in a given place and do not breed with individuals of other species, i.e., they are reproductively isolated.
- Mayr (1964) has defined species as 'a group of actually or potentially interbreeding poplulations, that are reproductively isolated from other such groups '.
- However interbreeding cannot be considered as a criterion for delimitation of a species, for the following reasons:
- Occasionally hybrids are formed in nature due to breakdown of the spatial mechanical, physiological and seasonal barriers between species.
- Interspecific hybrids have been raised artificially by man. The hybrids are mostly sterile, though a few are fertile.
- Mule — Female horse × Male donkey.
- Hinny — Male horse × Female donkey.
- Tigon — Male tiger × Female lion.
- Liger — Male lion × Female tiger.
In organisms where sexual reproduction is absent (e.g., monerans and some protists), other characteristics like morphology, cytology and biochemistry are considered.
Characteristics delimiting a species
- The 'member of a species are able to interbreed freely in nature and produce fertile offspring.
- The members of a species resemble one another more closely than they resemble members of other species.
- They show similarity in their anatomy and cytology; their Karyotypes are very similar.
- At the molecular level, they have similar genetic material, i.e., sequence of bases in DNA, amino acid sequence in proteins, enzymes and other biomolecules.
- The member of a species, whether present in the same population or spatially separated, are derived from a common ancestor.
Genus
- Genus is a group o related species that have more characters in common as compared to the individuals of species of other genera, e.g., Potato and brinjal belong to the same genus, Solanum, i.e., Solanum tubersom and Solanum melongena respectively.
- Similarly, lion, leopard and tiger belong to the genus Panthera, but to different species, i.e., Panthera leo, P.pardus and P.tigris respectively.
- A genus may be Monotypic, with only one species or it may be Polytypic with many species, e.g., Homo is monotypic. e.g., Solanum is polytypic
Family
- Solanum, Lycopersicum, Petunia and Atropa belongs to the family Solanaceae.
- Panthera and Felis (Cats) belongs to the family Felidae, while fox and dogs belongs to the family Cancidae.
Order
An order is an assemblage of families related to one another in a few characters.
- Solanaceae and Convolvulaceae belongs to the order Pelomoniales
- Felidae and Cancidae belongs to the order Carnivora.
Class
- Carnivora and Primata are the order of class Mammalia.
Phylum
- Phylum Chordata includes classes Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves and Mammalia.
Kingdom
- All Plants (Algae, Bryophytes, Pteridophytes, gynnosperms and angiosperms) are included in the kingdom plantae.
Table : Organisms with their Taxonomic Categories
| Taxa | Human | Housefly | Dog | Wheat | Mango | Tulsi |
|---|---|---|---|---|---|---|
| Kingdom/Phylum | Animalia | Animalia | Animalia | Plantae | Plantae | Plantae |
| Division | Chordata | Arthropoda | Chordata | Angiospermae | Angiospermae | Angiospermae |
| Class | Mammalia | Insecta | Mammalia | Monocotyledonae | Dicotyledonae | Dicotyledonae |
| Order | Primata | Diptera | Carnivora | Poales | Sapindales | Lamiales |
| Family | Hominidae | Muscidae | Canidae | Poaceae | Anacardiaceae | Lamiaceae |
| Genus | Homo | Musca | Canis | Triticum | Mangifera | Ocimum |
| Species | sapiens | domestica | familiaris | aestivum | indica | sanctum |