In this article we will discuss about Taxonomy which was started as “Folk Taxonomy” in earlier 15th century:- 1. History of Taxonomy 2. Phases of Taxonomy 3. Fundamental Components 4. Aims.
History of Taxonomy:
Plant taxonomy is one of the earliest disciplines of Botany. It was started as “Folk Taxonomy” in earlier 15th century but it has grown and gone very long way in the last 500 years. The concept and scope of Taxonomy has changed a Lot.
Though the flora of the earth was invented in the last three centuries yet the modern taxonomists are facing challenges. The tropical countries with rich flora are under threat. So far about 4,000,000 plants aspects are identified ox which 2, 86,000 are of angiosperms. Among the identified plants about seventy per cent being to tropical regions.
In the modern times, people are running for the applied sciences as cytology, genetics, experimental biology, ecology, molecular biology etc. but a few people are thinking of the basic or fundamental branches of botany like Taxonomy and Morphology.
It has become an old fashion. No applied branch can be approached without the proper identification of the Plant material on which he/she is working and for this, taxonomists are very much needed.
With the increased need for conservation of biological resources, the need tor biodiversity assessment during the last few years has increased. The trend has, however, reversed and taxonomic studies are being encouraged throughout the world.
Human interaction with the flowering plants is a fundamental biological activity where we rely on angiosperm for subsistence. The hunting-gathering human groups operating around in the very early times (20,000 years back) were more familiar with local flora, as they were getting food, medicines etc. from them Plant systematics has extremely deep cultural roots in all parts of the world African, Asian, and National American cultural groups carried a wealth of botanical lore with modern times (Plant Trivia Timeline), modern angiosperm classification systems have been derived from European base.
History of taxonomy begins with the categorization of useful plants of folk taxonomy People differentiated them as of economic value. This paved the way for herbal taxonomy.
Phases of Taxonomy:
The history can be studied in 4 phases which are as follows:
A. Exploratory Phase:
i. Theophrastus (370-285 BC) published “Enquiry into Plants. He proposed Crataegus, Daucus, Asparagus and Narcissus etc. in his work.
ii. Pliny (23-29) AD wrote multivoluminous Natural history of which 37 volumes are present. After 1000 years of Eclips in 16th century once again it revived.
iii. The first herbarium was established in 1553 in Padua (ITALY).
iv. In the middle of 17th century, herbaria were established in different parts of the world.
v. The important taxonomists of Linnean era are Ceasalipino (1519 1603) Bauhin (1560-1624), John Ray (1627-1705), de Tournefort (1656-1708) etc. Within their existing limits and knowledge they gave concept of species, synonymy, classification and nomenclature. They defined species as a natural group of organisms with invariant generalized or idealized pattern shared by all members of the group
vi. Linnaeus (1753) published Species Plantarum and introduced Binomial nomenclature which is a mile stone of plant taxonomy.
vii. The system of classification introduced by Linnaeus is Sexual system It was an artificial system on few characters.
viii. In exploratory phase Taxonomy was merely exploration and naming of species.
B. Consolidation Phase:
The phase is marked by publication of a number of monumental works on plant classification:
i. De Candolle (1778-1841) modified Linnaeus system
ii. Bentham and Hooker (1864) published Genera Plantarum where they have given natural system of classification which is of great practical use even now.
iii. Charles Darwin (1859) published On the Origin of Species, where in suggested the principle of natural selection and evolution of species.
iv. Dobzhansky (1937) published “Biological Species Concept”. Biological concept defined species as “a group of interbreeding population reproductively isolated from any other such group of population.”
Taxonomists realised that species are dynamic and:
(a) All populations tend to vary and no two species are ever alike.
(b) Some of these variations are adaptive and are of survival value.
(c) Forces of nature result in the extinction of some individual while others survive the same force.
(d) Some variations shown by individual within a population must be hereditary.
(e) The environments of individuals are not static.
i. Phylogenetic classification was based on the ideas of evolution. It started with Endichler (1804-1849), Eichler (1837-1887).
ii. Engler and Prantl (1887-1915) suggested semiphylogenetic system of classification in Die Natiirlichen Pfalenzen Familien.
iii. The first purely Phylogenetic system based on Dictas of Phylogeny was given by Bessey (1845-1915) which was improved by Hallier (1868-1938).
iv. John Hutchinson (1955) put forth his 24 principles of phylogeny and based on that suggested phylogenetic classification of value, in Families of flowering plants (1959).
v. The system was improved by contemporary Botanists like Takhtajan in Following Plants: Origin and Dispersal (1969); Cronquist in Evolution and Classification of Flowering Plants” (1981); Stebbins in Flowering Plant Evolution above the Species Level (1974) and Robert Throne in “A Phylogenetic Classification of Angiopermae” (1976) etc.,
vi. The classification was based on distribution, Ecology, Anatomy, Palynology Cytology and Biochemistry apart from Morphology.
vii. Techniques of herbarium preparation and presentation were developed and established.
C. Biosystematic Phase:
(i) The last fifty years have seen a qualitative improvement in the area of taxonomic concept and application by advancement of Biosystematics.
(ii) The “New systematics” is aimed at achieving the goal of “holotaxonomy”.
(iii) Huxley (1940) proposed the term “New systematics.”
(iv) Camp and Gilly (1943) proposed the term “Biosystematics” to new systematics.
(v) The number, size and shape of chromosomes were considered by cytotaxonomists as very reliable taxa.
(vi) The development of techniques like two dimensional paper chromatography, identification of chemical substances in plants as secondary metabolites led to the development of “Chemotaxonomy”.
(vii) The new techniques can give details as amino acid sequencing and determining nucleotide sequence in DNA and RNA.
D. Encylclopaedic or Holotaxonomic Phase:
Information is gathered, analysed, and a meaningful inference is drawn for understanding phylogeny:
i. Collection of data, analysis and synthesis are the jobs of an independent discipline of taxonomy, i.e., Numerical Taxonomy.
ii. Numerical Taxonomy or quantitative taxonomy is based on numerical evaluation of the similarity between groups of organisms and the ordering of these groups into higher ranking taxa on the basis of these similarities.
Exploratory and Consolidation phase are considered as Alpha taxonomy while Biosystematic and Encyclopaedic phase are considered as Omega Taxonomy.
Fundamental Components of Taxonomy:
Taxonomy is a fundamental science. With the increase in knowledge various components developed.
(i) Alpha Taxonomy (Descriptive Taxonomy):
The aspect of Taxonomy is concerned with the description and designation of species. Typically on the basis of morphological characters, it developed in 19th century. It is started with work of Tournefort, de Jussieu and Linnaeus.
(ii) Beta Taxonomy (Macrotaxonomy):
The arrangement of species into hierarchical system of higher categories or taxa. It developed in 20th century.
(iii) Gamma Taxonomy:
Aspect of taxonomy concerned with intraspecific population and with phylogenetic trends are included in gamma taxonomy. An attempt is made to account for the origin and development of species. To determine the origin of a species, a taxonomists has to depend on the species of paleobotany which includes all taxa of extinct plant groups.
(iv) Omega Taxonomy:
It is an ultimate perfect system, based upon all available characters.
The best is the concept of Alpha-Omega Taxonomy. As alphataxonomy forms the basis of biology while the final accumulation of all data is ultimately incorporated into Omega taxonomy.
Aims of Taxonomy:
There are three main aims of taxonomy, i.e., Identification, nomenclature and classification.
There are two main approaches:-
(a) Empirical Approach:
It is based on practical aspects, observation of characters etc.
(b) Interpretive Approach:
The classification is based on interpretation and evolution of a taxon, e.g., phylogenetic system.
Modern taxonomy combines both approaches with the following aims:
(i) To provide a convenient method of identification and communication.
(ii) To provide classification which is based on natural affinities of organisms as far as possible.
(iii) To provide an inventory of plant taxa by means of flora.
(iv) To detect evolution at work, discovering its process of interpreting into results.
(v) To provide an integrating and unifying role in the training of biology students regarding the relationships between many biological fields and data gathering science.
Summary of history of classification may also be taken in the following way:
(1) Ancients (2000 BC – 1500 AD.)
Theophrastus and essentialism:
Classification by habitat, Emphasis on genus.
‘Ladder of life’ or ‘great chain of being’ or ‘Scalae Naturae’.
(2) Herbalists (1500 AD – 1580 AD)
Pledanius Disorides (C. 40 – 90 AD):
De Materia Medica and connection of Greek medicine, plants and classification.
German Herbalists and their herbals:
Classification of medicinal properties.
(3) The pivotal period:
Beginning of natural thought (1580AD – 1800AD) Andrea Caesalpino
John Ray:
The concept of ‘class’ [orders],
Pierre Magnol:
The concept of family.
Carolus Linnaeus (Carl Linnaeus):
Sexual system of classification in Species Plantarum.
Species Plantarum:
The ultimate mechanical or artificial system.
(4) Natural system (1760AD-1880AD):
Antoine de Jussieau John Bentham and Joseph Dalton Hooker.
(5) Period of Phylogentic systems (1859AD-Till date):
Charles Darwin:
Impact of On the Origin of Species for classification.
Adolf Engler & Karl Prantl:
“Die NatUrlichen Pflanzen familien”. Salix as primtive.
Charles Bessey:
Dicta and cactus classification scheme considered Magnolia = Primitive.
John Hutchinson. 24 Principles of Phylogeny.
Arther Cronquist Armen Takhtajan Robert Throne Rolf Dahlgren.
6. Phylogenetic and Molecular systematics:
Phylogenetic and Molecular systematics (1993-till date) ongoing role in redefining classification.
1993:
The first major classification based on DNA (rbcL of cpDNA): rbcb sequencing study called Treezilla that redefined angiosperm systematics.
1998 & 2003 APG classification system:
The angiosperm phylogenry group.
Issues in Phylogenetic classification: grouping in hierarchical (“Linnaean”) system:
i. Problem of character convergences in defining higher taxonomic grouping and subjective choice of characters.
ii. Named groups are monophyletic (ancestors of all descendants) or at least paraphyletic but not polvphyletic.
iii. Name of species remain the same but conveys knowledge of natural affinities and evolutionary relationships.
iv. All groups are not named.
v. Ranks are arbitrary and not of same age.
“Rankless” classification system – The phylocode system (July 2004: 1st convention):
(i) Replace ‘Linnaean’ hierarchical system with ‘phylogenetic classification system and nomenclature.
(ii) Groups given unranked names.
(iii) Groups defined by ancestry i.e., phylogenetic tree.
(iv) Groups described/diagnosed by a character(s) are the branch of the monophyletic group.
(v) No types but specifier for nodes or trees.
Deme Terminology:
Gilmour and Gregor (1939) proposed the new system of terminology providing an infinitely flexible series of categories used to define any group of individuals. The system is known as Deme terminology It and does not consider genus, species etc. Deme implies to a group of related individuals of a particular taxon. The precise meanings of the term are provided by various prefixes.
Topodeme:
A deme occurring within a specified geographical area.
Ecodeme:
A deme occurring within a specified kind of habitat.
Gamodeme:
A deme composed of individuals which interbreed in nature.
Phenodeme:
A deme differing from others phenotypically.
Plastodeme:
A deme differing from others phenotypically but not genotypically.
Genodeme:
A deme differing from others genotypically.
Autodeme:
A deme composed of predominantly self fertilizing or autogamous individuals.
Endodeme:
A deme composed of predominantly closely in-breeding (endogamous) but dioecious individuals.
Agamodeme:
A deme composed of predominantly apomictic (non-sexually reproducing)individuals taxonomy of angiosperms.
Clinodeme:
A deme which together with other such deme forms a gradual variational trend over a given area.
Cytodeme:
A deme composed of individuals all with the same karyotype (chromosome morphology).
Genoecodeme:
An ecodeme differing from others genotypically (Ecotype).
Plastoecodeme:
An edodeme differing from others phenotypically and not genotypically (Ecophene).