|TABLE OF CONTENTS|
5. Taxonomic Categories
6. Species Concept
7. Type of Taxonomy
8. History of Taxonomy
Taxis = orderly arrangement, nomos = law
Taxonomy Definition: “Taxonomy is the study of principles and procedures of classification.”
Fig: PlantTaxonomy includes study of following 4 points:
(1) Identification: Identification of living organisms
(2) Nomenclature: Nomenclature of living organisms
(3) Classification: Classification of living organisms in groups
(4) Affinities: Study of inter relationship between living organisms
“Systematics is a branch of Biology that deal with cataloguing plants, animals and other organisms into categories that can be named, remembered, compared and studied.”
- Study of only one organism of a group provides sufficient information about the remaining members of that group. Scientists connected with the study of systematics are called systematists or taxonomists.
- The term "Systematics" was proposed by Linnaeus.
- It includes a description of external morphological characters of plants or living organisms.
Example: Morphological characters of Root, Stem, Leaves, Flowers.
Basics of Systematic Study
1. Characterization: The organism to be studied is described for all its morphological and other characteristics.
2. Identification: Based on the studied characteristics, the identification of organism is carried out to know whether it is similar to any of the known group or taxa.
3. Classification: The organism is now classified on the basis of its resemblance to different taxa. It is possible that the organism may not resemble any known taxa or groups. A new group or taxon is raised to accommodate it.
4. Nomenclature: After placing the organism in various taxa, its correct name is determined. If the organism is new to systematics, it is given a new name based on rules and conventions of nomenclature.
Fig: Difference between taxonomy and systematicsNOMENCLATURE
1. Polynomial system:
- According to this system, name of any plant consists of many words.
- For eg. Caryophyllum–Cqryophyllum saxatilis folis gramineus umbellatis corymbis
2. Binomial system:
- Binomial system was first proposed by Gaspard Bauhin in his book - "Pinax Theatre Botanica."
- Principle of Priority: The nomenclature is done by principle of priority. If two names are proposed for any plant after the 1753, the valid name is the earlier name proposed just after 1 May, 1753.
ICBN (International Code of Botanical Nomenclature):
Fig: ICBN full form
- ICBN - Book of rules of nomenclature.
- Collection of rules regarding scientific - nomenclature of plants is known as ICBN.
- ICBN was firstly proposed by – Sprague, Hitchcock, Green (1930)
- ICBN was first accepted in 1961.
- 12th International congress, Leningrade, revised ICBN in 1975.
- After revision, it was republished in 1978. So that ICBN was published two times
- ICNB = International Code of Nomenclature 'for Bacteria
- ICVN = International Code of Viral Nomenclature
- ICNCP = International Code of Nomenclature for Cultivated Plants
Main rules of ICBN
- According to binomial system name of any species consists of two names:
(i) Generic name - Name of genus
ii) Specific epithet - Trival name
Example: Specific Name - Mango; Generic Name - Mangifera indica
- In plant nomenclature (ICBN) tautonyms are not valid i.e. generic name and specific name should not be same in plants.
Example: Mangifera Mangifera
But tautonyms are valid in animal nomenclature (ICZN-International Code of Zoological Nomenclature). Example: Naja naja (Indian cobra), Rattus rattus (Rat)
- Length of generic name or specific name should not be less than 3 letters and not more than 12 letters.
Example: Mangifera indica
- First letter of generic name should be in capital letter and first letter of specific name should be in small letter.
Example: Mangifera indica
But if specific name is based on the name of some person, its first letter should be in capital letter.
Example: Isoetes Pantii
- When written with free hand or typed, then generic name and specific name should be separately underlined. But during printing name should be italized.
- Name of the scientist (who proposed nomenclature) should be written in short after the specific name.
Example: Mangifera indica Lin
- Name of the scientist should be neither underlined nor written in italics, but written in roman letters (simple alphabets).
- If any scientist has proposed wrong name then his name should be written in the bracket and the scientist who corrected the name should be written after the bracket.
Example: Tsuga canadensis (Lin.) Salisbury
Note: Linnaeus named this plant as Pinus canadensis.
- Scientific names should be derived from Latin or Greek languages because they are dead languages.
- Type specimen (Herbarium Sheet) of newly discovered plant should be placed in herbarium (Dry garden).
- Standard size of herbarium sheet is 11.5 × 16.5 inches.
3. Trinomial system:
- Proposed by Huxley and Stricklandt. According to this system name of any plant or species is composed of three names -
(i) Generic name
(ii) Specific name
(iii) Subspecific name (Name of variety)
- When members of any species have large variations then trinomial system is used. On the basis of dissimilarities, this species is classified into sub species.
Example: Brassica oleracea var. botrytis (Cauliflower), Brassica oleracea var. capitata (Cabbage), Brassica oleracea var. caulorapa (Knol-Khol)
- The art of identifying distinctions among organisms and placing them into groups that reflect their most significant features and the relationship is called biological classification.
- The purpose of biological classification is to organize the vast number of known organisms into categories that could be named, remembered and studied.
According to"A.P. de Candolle", Classification is of two types:
(A) Empirical Classification
- In this type, the actual nature or character of plants is not considered.
- Plants are classified on the basis of their alphabetical order, i.e. on the basis of the name of plant.
- On the basis of name, plant kingdom can be classified in 26 groups. (Their are 26 alphabets in English - According to this classification, all plants having same initial alphabet, are placed in one group.
Example: If the name of plants, starts from 'A', then it is placed in "A -group". Similarly if it starts with 'B', then it is placed in 'B - group
- This is not a true classification. It has only one application :- "Listing of flora".
- If any scientist, writes the flora of a particular area then he uses empirical classification.
- Flora → Plants growing in a particular area.
- Two books in which flora of India is written:
(i) Flora British Indica → By J.D. Hooker
(ii) Flora Indica → By William Rouxburgh
(B) Rational Classification
In this classification, plants are classified on the basis of their actual character or nature i.e. by viewing the characters.
Type of rational classification:
(i) Practical classification:- In this type of classification, plants are classified on the basis of their economic importance. In this type of classification morphology of plants is not considered. Example: Oil yielding plants (Coconut, Walnut), Soybean Fibre yielding plants (Jute, Cotton), Medicinal plants (Rauwolfia, Cinchona, Eucalyptus)
- Example: Turmeric - Multi uses plant, it gives both medicines and spices.
Note: In this classification, any one plant can be a member of more than one group.
(ii) Artificial classification:- In this type of classification plants are classified on the basis of one or two morphological characters. i.e. overall morphology is not considered.
Example: Classification proposed by Linnaeus is Artificial
Linnaeus classified plant kingdom on the basis of only two characters:
On the basis of stamens and style, Linnaeus classified plant kingdom in to 24 classes
- Monandria — Those flowers in which only 1 stamen is present.
- Diandria — 2 stamens in flower
- Triandria — 3 stamens in flower
- Polyandria — Many stamens
- Nonandria/Cryptogamia — No stamens
Note: Linnaeus divided flowering plants into 23 classes starting with class monandria with a single stamen, (Example - Canna) and plants with twenty or more stamens attached with calyx were assigned to class Icosandria. He also included all non-flowering plants such as algae, fungi, lichens, mosses and ferns in a separate class called Cryptogamia or nonandria.
(iii) Natural classification:- In this type, plants are classified on the basis of their complete morphological characters of stem, root, leaves, flowers etc. Maximum characters are taken as base in this classification.
Fig: Brassica oleracea
(iv) Adansonian system or phenetic classification or Numerical classification:-
- Numerical taxonomy was developed by Skol and Sneath.
- It uses characters in form of numbers, mathematical formulas and statistics to study the relationship among organisms
- In this, importance to any one character is not given, all characters have same importance. While in natural classification floral (reproductive) characters have more importance than vegetative (root, stem, and leaves) characters.
(v) Phylogenetic system of classification
- It was first proposed by a british scientist John Hutchinson.
- The basis of phylogenetic system of classification is the ancestral history of the organisms. It is based on the theory that organisms with most common characteristics have originated from a common ancestor.
- Taxonomic categories or taxa (singular – taxon) are the level that have created to group similar organisms
There are seven main taxonomic categories.
Fig: Taxonomic categories1. Species: Species (used both as singular and plural) is a natural population of individuals or group of population which resemble one another in all essential morphological and reproductive characters so that they
are able to interbreed freely and produce fertile offspring.
The scienctific name of mango is Mangifera indica, where “Mangifera” is the genus and” indica” is the species.
The scientific name of potato is Solanum tubersum, where “Solanum” is the genus and “tubersum” is the species.
2. Genus: It is a group or assemblage of related species which resemble one another in certain correlated characters. Correlated Characters are those similar or common features which are used in delimitation of a taxon above the rank of species. All the species of a genus are presumed to have evolved from a common ancestor.
3. Family: It is taxonomic category which contains one or more related genera. All the genera of a family have some common features or correlated characters. They are separable from genera of a related family by important and characteristic differences in both vegetative and reproductive features.
For example the genera of cats (Felis) and leopard (Panthera) are included in the family felidae.
4. Order: The category includes one or more related families. Thus the family solanaceae is placed in the order polemoniales along with four other related families (convolvulaceae, boraginaceae, hydrophyllaceae and polemoniaceae).
Similarly, the families felidae and canidae are included under the order carnivore along with hyaenidae (hyaenas) and ursidae (bears).
5. Class: A class is made of one or more relates order. For example, the class dicotyledoneae (dicotyledonae, dicotoyledons) of flowering plants contains all dicots which are grouped into several orders.
- Examples: Rosales, passiflorales, polemoniales, sapindales, ranales, etc.
Likewise, class mammalian of animals includes all mammals which range from bats (order chiroptera), kangaroos (order marsupialia), - rodents (order rodentia), whales (order cetacean), and carnivores (order carnivora) to great apes and man (order primate).
6. Division or phylum: It is a category higher than that of class. The term phylum is used for animals while division is commonly employed for plants. A division or phylum is formed of one or more classes. The phylum chordate of animals contains not class mammalian but also aves (birds), reptilian (reptiles), amphibian (amphibians), cyclostomata, chondrichthyes, osteichthyes (fishes) etc.
7. Kingdom: It is the highest taxonomic category. All plants are included in kingdom plantae while all animals belong to kingdom animalia. There are some extra categories, like sub division, sub order, sub family, tribe, sub tribe, etc. They are not regularly used. They are used only when they are needed.
John Ray:- Proposed the term and concept of species.
To explain the species different concepts were proposed, which are as follows:
(A) Biological concept of species:-
- Mayr proposed the biological concept of species.
- According to Mayr "All the members that can interbreed among themselves and can produce fertile off spring are the members of same species" But this definition of Mayr was incomplete because this definition is applicable to sexually reproducing living beings because there are many organisms that have only asexual mode of reproduction suc as bacteria and mycoplasma.
- The main character in determination of any species is interbreeding. But this character is not used in taxonomy. In taxonomy, the determination of species is based on other characters such as morphology.
- In higher plants, the determination of species is mainly based on the morphology of flower (floral morphology). because floral (reproductive) characters are more conservative as compared to vegetative (Root, Stem, Leaf) characters i.e. they do not show major changes.
- When the species is determined on the basis of interbreeding then it is called as biological species.
Example - All the humans in this world can interbreed among themselves.So all the humans are the members of one biological species.
- When the determination of species is based on other characters then it is called as taxonomic species.
(B) Static concept of species :-
- The static concept of species was proposed by Linnaeus. According to Linnaeus "species is un-changeable" i.e. there is no change in the character of species. The species of present day are same as they were in past and they will remain same in future.
- Linnaeus believed in the "Theory of Special creation"
Father Suarez - gave the principle of special creation. According to this theory "All the living organisms are created by God (Every life is created by God) and God gave the basic size and shape of all living organisms, they are still present in their actual former form. But Lamarck rejected this hypothesis.
Fig: Father Suarez(C) Dynamic concept of species:-
- It was proposed by "Lamarck".
- According to this concept "Species is always changeable". Changes always occur in the characters of species from one generation to next generation. And these changes are known as "evolution".
(D) Typological concept:-
- It was proposed by "Aristotle" and "Plato".
- According to this concept "There is a definite type or pattern of characters in the each species of every living organism and all the members of species show maximum resemblance with this pattern. (Typological concept is based on single individual of species) The species in which a fixed pattern of characters is present are called as monotypic species.
Example - Bacteria, BGA
- In many species, more than one type or pattern of characters are present. These are called "Polytypic species" or "Macrospecies".
Example - Brassica oleracea → Cauliflower, Cabbage, Knol - khol.
Polytypic Species are of three types:
1. Biotype – Members of same species inhabiting similar environment and having some genetic variations are known as biotypes. Variations found in these members are permanent. These members cannot interbreed among themselves.
Example - Cauliflower , Cabbage, Knol –Khol are three biotypes of one species.
2. Ecotypes – Members of same species inhabiting different environment and having some genetic variations are known as ecotypes. Variations are permanent. These members can interbreed among them selves but due to geographical barrier they are unable to interbreed.
Example - Crow (Corvus splendens) found in different regions are ecotype of one species
Corvus splendens splendens – Indian crow
Corvus splendens insolens – Myanmar crow
Corvus splendense protegatus – Srilankan crow
3. Ecads or Ecophenes – Members of same species having some non genetic variations due to change in environment. These variations are temporary.
Example -Every living being
Note:- This hypothesis is believed to be most acceptable.
SOME DEFINITION RELATED TO SPECIES
1. Linneon species:- Those taxonomic species whose determination is based on morphology. They are called as linneon species. They are also called morpho-species or taxonomic species.
Example - Most of species in taxonomy are linneon species
2. Microspecies or Joardan's species:- Those species in which variations are very less. They reproduce asexually so they have very less variations.
3. Sibling species or Cryptic species:- Members of species which are morphologically similar but reproductively isolated are known as sibling species i.e. they can not interbreed among themselves.
Sibling species is one taxonomic species (because these members have similar morphology) but they are different biological species. [Because they can not interbreed]
Example - Brassica oleracea
4. Allopatric species:- The species found in different geographical regions and have geographical barriers between them are known as allopatric species. Geographical barriors like hills, oceans, Himalyan Mountains.
5. Sympatric species:- The species found in similar geographical regions.
6. Allochronic species:- The species found in different time periods or era.
Example - Man and Dinosaurs
7. Synchronic species:- Those species that are found in same era.
Example - Dinosaurs and Archaeopteryx
Fig: Archaeopteryx8. Palaeo species:- Those species that are extinct now and are found in the form of fossils.
Example - Dinosaurs
9. Neontological species:- Those species which are living presently.
TYPE OF TAXONOMY
1. Alpha taxonomy or classical taxonomy: It is based on external morphological characters of plants.
2. Beta taxonomy: Besides external morphology, it also includes internal characters like embryological, cytological, anatomical characters etc.
3. Omega taxonomy: Omega taxonomy has widest scope. It is based on all the information or data available about plants.
4. Cytotaxonomy: The use of cytological (cellular) characters of plants in classification or in solving taxonomic problems is called cytotaxonomy. Cytological characters constitute an important aid to plant taxonomy, especially in determining affinities at the generic and intrageneric levels.
5. Chemotaxonomy: The uses of chemical characters of plants in classification or in solving taxonomic problems is called chemotaxonomy or chemical taxonomy. It is based on the chemical constitution of plants. The fragrance and taste vary from species to species.
The basic chemical compounds used in chemotaxonomy are alkaloids, carotenoids, tannins, polysaccharide, nucleic acids, fatty acids, amino acids, aromatic compounds etc.
6. Karyotaxonomy: Based on the characters of the nucleus and chromosomes. Pattern of chromosomal bands (dark bands and light bands) is most specific characters.
HISTORY OF TAXONOMY
(1) Aristotle (382 B.C.):- Father of biology & father of zoology
Fig: Aristotle(2) Theophrastus
- Time - 370 - 285 B.C.
- He is known as father of ancient plant taxonomy and father of botany.
- Both Theophrastus & Aristotle are Greek political philosophers.
(3) Carolus Linnaeus [1707 - 1778]
- His real name was - Carl Von Linne
- On the basis of work in Latin language, he changed his name to Carolus Linnaeus. He was the Swedish scientist
- He is known as the father of taxonomy, father of plant taxonomy and father of animal taxonomy.
- Linnaeus gave the two kingdom system classification. He grouped plants and animals into kingdom Plantae and kingdom Animalia respectively.
- Linnaeus wrote many books. Some important books are:-
(i) Hortus uplandicus - First book
(ii) Flora lapponica
(iii) Philosophia botanica
(iv) Critica botanica
(v) Systema naturae (1737)
(vi) Genera plantarum
(vii) Species plantarum - last book (1753)
(4) A.P. De Candolle
- He wrote the book "Theories Elementaire de la botanique". He was the first to propose the significance of vascular tissue in taxonomy.
- On this basis of vascular tissue he classified plants into two groups:
(i) Cellular plants (Non-vascular plants) - this group includes Thallophyta and Bryophyta
(ii) Vascular plants - This group includes Pteridophyta, Gymnosperm and Angiosperms.
(5) George Bentham (1800 - 1884) and Joseph Dalton Hooker (1817 - 1911)
- Both Bentham and Hooker were related to Royal botanical garden.
- Scientists working in botanical garden are known as curator.
- They wrote the book "Genera plantarum" (1862 - 1883). In this book, Bentham and Hooker gave the biggest and natural classification of spermatophyta i.e. plants with seeds.
- In Genera plantarum, there is description of 202 families. In it, basically the description of seeded plants is present.
Fig: Spermatophyta classification
Merits of Bentham and Hooker classification:
- The classification of Bentham and Hooker was natural formal.
- The classification of Bentham and Hooker was mainly based on the floral characters. This was very appreciable because floral characters are more stable than vegetative (root, stem, leaves) characters.
- It is the simplest classification. Therefore the arrangement of all plants in the botanical gardens and herbarium of the world is based on it. Although it is not the best classification but yet the arrangement of plants in botanical gardens and herbariums is based on it, because it is the simpler one. The main reason for its simplicity is that this classification is based on actual observations.
Demerits of Bentham and Hooker:
- In this classification the phylogeny of plants is not considered, because in it, gymnosperms are placed in between dicots and monocots. The sequence of evolution is as follows:- Phylogeny = Gymnosperm → Dicots → Monocots
(6) A.W. Eichler
- Syllabus de vorlesungen uber phanerogamen kunde - Book written by Eichler.
- In this book, Eichler gave the first phylogenetic classification of plant kingdom.
- Eichler classified plant kingdom into five divisions and arranged them in the order of evolution (Phylogeny). Thallophyta → Bryophyta → Pteridophyta → Gymnosperm → Angiosperm
(7) Engler (1844 - 1930) & Prantl (1849 - 1893):-
- Book - "Die Naturlichen Pflanzen Familien"
- He gave the phylogenetic classification of plant kingdom. This classification was more phylogenetic as compared to Eichler's classification.
(8) Oswald Tippo:-
- Proposed the biggest phylogenetic classification of plant kingdom.
- This classification is the complete classification of plant kingdom.
- This is the most acceptable classification for books and study.
(1) Cyanophyta – B.G. Algae
(2) Euglenophyta – Euglenoids
(3) Chlorophyta – Green algae
(4) Chrysophyta – Yellow - Green - algae
(5) Pyrrophyta – Dinoflagellates & Diatoms
(6) Phaeophyta – Brown algae
(7) Rhodophyta – Red algae
(8) Schizomycophyta – Bacteria
(9) Myxomycophyta – Slime molds (false fungi)
(10) Eumycophyta – True fungi
These ten divisions include three types of organisms:
(1) Algae = 7 - division
(2) Bacteria = 1 - division
(3) Fungi = 2 - division
Fig: Embryophyta division
Note : Tippo did not use the word pteridophyta.
(9) Karl Menz:
- He showed the importance of serology in taxonomy.
- Similarities and dissimilarities in the structure of proteins help to know the phylogenetic relationship of living beings. Living organisms which are phylogenetically close relatives have more similarities in their proteins. Organisms which are distantly related have different proteins.
Note: Phylogenetic relationship of plants and animals can be established by animal serum. Serology indicates that chimpanzee is the closest relative of man.
- Haeckel gave the three kingdoms (Protista, Plantae, Animalia) system of classification.
- Haeckel established the kingdom Protista.
- The term 'Protista' was given by C. Cuvier.
- Haeckel grouped those living organisms in Protista which did not have tissues.
- Kingdom Protista → Prokaryotes, Protozoa, Porifera, Algae & fungi
- First tissue was originated in animal kingdom in → Coelenterata
- First tissues was originated in plant kingdom in → Bryophyta
- He gave the “Four kingdom system of classification”.
- Mychota:- Dougherty & Allen gave the name "Monera" to Mychota of Copeland. All the prokaryotes are grouped in Monera Protista or
- Protoctista:- Copeland grouped those eukaryotes in protista, which are visually different than normal plants and animals. e.g. Brown algae, Red algae, Fungi, Protozoa
- Plantae or Metaphyta:- Remaining all eukaryotic plants are grouped.
- Animalia or Metazoa:- Remaining all eukaryotic animals are grouped.