In this article we will discuss about Taxonomy:- 1. Need and Importance of Taxonomy 2. Different Aspects of Taxonomy 3. Phases.
Need and Importance of Taxonomy:
With the huge variety of plants surrounding us, it is extremely essential to pinpoint a particular plant of our interest by noting the similarities or differences with other plants. A biologist studying a particular plant needs to know his field of study.
Thus it becomes extremely necessary that the plant is first identified, given a proper name so that he can communicate his ideas about it, and also know the group to which the plant belongs.
These three activities are, in fact, the main functions of taxonomy. Thus taxonomy, which is probably the oldest of sciences, is the science of classification, including its bases, principles, rules and procedures.
Its general purpose is to arrange plants in such a way as to provide an information retrieval system, i.e. the name and rank or position in an ordered hierarchy, which tells us something about the plant. It comes from two Greek words, taxis meaning arrangement and nomous meaning law or rule.
Thus, taxonomy means classification following certain rules or, principles. But it is very important to note that a plant’s name is the key to its literature, and grouping can only be possible when its identity is revealed and are named for the sake of convenience and communication of ideas about it.
The term taxonomy was first introduced to the plant science in 1813 by A. P. de Candolle, which meant the theory of plant classification. But later this term became more inclusive and at present it includes identification of plants, their nomenclature and classification. Traditionally taxonomy was based largely on gross morphological features of a plant.
However now virtually all other scientific information is used from branches like anatomy, genetics, cytology, chemistry, reproductive biology, ecology, physiology, molecular biology, etc. (Fig. 1.1). Hence taxonomy is a very dynamic and synthetic science and is the basic to all other sciences.
At the same time it is dependent upon them, i.e. the information used by taxonomists is gathered using information from other disciplines such as genetics, ecology, morphology, anatomy, physiology, etc.
Different Aspects of Taxonomy:
The three functions of taxonomy include, identification, nomenclature and classification (Fig.1.2). Its main aim is to provide a convenient method of identification and communication about a taxa and provide a classification which is based on natural affinities of plants as far as possible.
The word ‘taxon’ (taxa) was first used by a German Biologist Adolf Meyer in 1926 for animal groups. It was later proposed for the plant system in 1948 by Herman J. Lam. It is a taxonomic group of any rank, e.g. family, genus, species, subspecies, etc.
Identification of a taxon is a prerequisite for any study based on it. It is the determination of a taxon based on overall similarities and differences with other taxa. Identification is generally done by comparing representative specimen of a given taxon with the help of key descriptions, illustrations, etc.
Sometimes, the specimen may not agree or compare with the existing predetermined specimen. In such a case it is taken to be new to science. Identification is thus assignment of additional unidentified plants to a correct rank once a classification has been established. It is the determination of a name for a specimen. This also implies its rank.
Once the taxon has been identified, it becomes necessary to give it a scientific name. Thus, nomenclature is the naming of a taxon correctly. It is a precise and universal system of rules used by all botanists of the world for naming newly discovered plants.
Often constant study of plants results in differences of opinion concerning past work. This often results in splitting, uniting, changing ranks etc., all of which may affect the plants name. Thus, universal rules are needed to determine the correct name for a plant and the rules for naming the plants are governed by the International Code of Botanical Nomenclature (ICBN). A new name is given to a new taxon.
Keeping in view, the enormously high number of plant species, it is impossible for any one to study all plants individually. To overcome this problem, the plants can be placed into small or large groups based on their similarities and differences, and then arranged in a sequential manner into categories according to their levels, and each category given a name following the rules of nomenclature.
For example, similar plants may be grouped under a “species“, similar species under a “genus“, and so on.
Classification is thus, the arrangement of groups of plants with particular characteristics by rank or position according to certain criteria, and placing them within the taxonomic hierarchy. It includes the determination of position or rank for new taxa as well as old taxa, which have been remodelled, divided, united, transferred or altered in rank.
There are basically three kinds of classification: artificial, natural and phylogenetic :
It is the classification that is based on one or a few easily observable characters such as habit, colour, form, etc., often irrespective of their affinity.
It is the classification that is based on overall similarity, mostly on gross morphology.
These classification however, are not mutually exclusive but often overlap in practice. It is the classification based on common evolutionary descent.
It is the part of classification that involves the arrangement of plants into related groups. It is the scientific study of the kinds and diversity of plants and the relationships among them if any, and includes not only the traditional activities of taxonomy but also the investigation of such things as evolution, speciation, natural variation, reproductive biology, and a variety of biological phenomena.
According to Radford (1986) systematics is the study of phonetic, genetic and phylogenetic relationship among taxa.
(e) Molecular Systematics:
Molecular systematics is that part of systematics, which utilizes data from nuclear, chloroplast or mitochondrial DNA, to elucidate phylogenetic relationships between plants. Gene sequences obtained from protein-coding genes, ribosomal RNA or non-coding spacer regions are often used in molecular systematic studies.
Other DNA-based methods such as Restriction Fragment Length Polymorphism (RFLP) and Random Amplified DNA Polymorphisms (RAPD) “fingerprinting” are used to study problems or issues on genetic diversity (which has implications for conservation and management), the detection of hybrids, and taxonomic delimitation at the level of species.
Phases of Taxonomy:
Classification of a taxon, is generally achieved in four successive phases, as formulated by Davis and Heywood (1963):
(a) The Pioneer (or Exploratory) Phase:
This is the discovery and collection phase and different members of a taxon are collected from different parts of the world (exploration) and identified, at least provisionally.
(b) The Consolidation Phase:
This is the synthesis phase mostly based on morphology. This phase deals with the study of the plant material in the field as well as in the herbarium. All the new groups, if invented, are described. Thus a compilation of a flora or a monograph is done in this phase.
(c) The Experimental or Bio-Systematic Phase:
This deals with a wide variety of things and a more thorough knowledge of a taxon based on analysis of a wide variety of things such as the geographical variation, chemical studies, cytogenetic studies, physiological features, fertility relationships, evolutionary patterns and other population studies.
(d) The Encyclopaedic or Holotaxonomic Phase:
This is a coordination of the three phases mentioned above and involves the analysis and synthesis of all information and types of data to develop classification systems based on phylogenetic relationships. The first two phases corresponding to the “alpha” classification are mainly descriptive and based on gross morphological features.
The last two phases correspond to the “omega” (to) classification. The data for these phases are accumulated from researches in the field, laboratory, garden, herbarium and library, and may be analysed with the help of computers.