Plant Taxonomy- Definition, History, Classification, Types

Taxonomy was recognized as a general subject only in 1813 by A.P.de Candolle. His famous work describes in the book of which name is Theorie elementaire de la botanique. Taxonomy is a combination of Greek words ‘taxis’ means arrangement and ‘nomos’ means rules or law. Taxonomy deals with the identification, nomenclature, and classification of plants.

Classical Taxonomy

  1. The Classical Taxonomy is also known as “Orthodox Taxonomy”.
  2. Classical Taxonomy generally deals with operational procedures such as identification, nomenclature, & classification of species.
  3. Classical Taxonomy is based on morphological characters & anatomical data along with geographical distribution of species the information is collected from the herbarium.

Systematics

The term systematic first given by Linnaeus. Systematics is based on the classification of plants and arranging them into hierarchical order. Systematic is the scientific study of plants and their evolutionary history. Study of Systematics and taxonomy both known as systematic biology.

Biosystematics

  1. Another name of biosystematics is Experimental Taxonomy or New Systematics.
  2. Biosystematics deals with the taxonomic study of the organisms from the standpoint of populations rather than individuals & of the evolutionary process found along with populations.
  3. Biosystematics is largely based on genetically, cytological & ecological aspects of plants and involves study in experimental gardens & infield.
Plant Taxonomy
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History of Plant Taxonomy

Theophrastus

  • Theophrastus is a “Father of Botany ”. Theophrastus plant divided into four categories.
    1. Herbs
    2. Sub-shrubs
    3. Shrubs
    4. Tree

Albertus Magnus

  • He separated vascular plant from non-vascular and also monocot & dicot.

John Ray

  • He suggested a scheme of classification of plants.

Carolus Linneaus

  • Father of Taxonomy
  • Proposed a Binomial system of nomenclature.
  • In binomial nomenclature, the first name is the genus name and the second name is the species name.

Antoine Laurent de Jussieu

  • Proposed a classification system based on natural characters.

Five classification system

Artificial System of Classification

  • Artificial System of Classification gave by Secundus, Theophrastus, Dioscorides Magnus.
  • This classification system gives emphasis on observable characters such as color, number, habit, form, or same characters.

Mechanical Classification

  • Mechanical Classification proposed by Bauhin, Ray, Tournefort & Linneaus.
  • Mechanical Classification based on one or a few selected taxonomic characters to group taxa.

Natural Classification

  • Natural Classification proposed by M. Adason and extensively used by Bentham & Hooker in the classification system.
  • In this classification system based on overall morphological similarity & taxonomic characters are used to group taxa.

Phenetic Classification

  • Phenetic Classification has given by Sneath & Sokal in 1973.
  • Phenetic classification uses the whole similarity in terms of phonetic relationship based on data from all available sources such as morphology, ultrastructure studies & another relevant branch of study.

Phylogenetic System of classification

  • Phylogenetic System of classification based on the evolutionary descent of a group of organisms. The relationship is shown through a phylogram, phylogenetic tree, or cladogram.

Angiosperm Phylogeny Group system (APG System)

APG is the first version of a modern mostly molecular-based system of plant taxonomy. It is the first time published in 1998 known as APG I. then published in 2003 known as APG II and in 2009 published APG III. APG classification is mainly based on the synthesis of knowledge about the relationship of angiosperms, obtained from morphological to molecular data and using the phylogenetic methods. In the APG classification system, only monophyletic groups should be recognized. Above the level of orders and families, the term “clade” is used more generally.

Advantages of APG

  • APG system based on the principle of monophyly, phylogenetic, anatomical, embryology, phytochemistry, molecular formal name have been given only to those group where monophyly has been firmly established.
  • To reduced the problem of paraphyly,  the traditional separation of angiosperms into monocots and dicots has been discarded. Various groups of monocots have been placed in between primitive dicots and advances dicots.

Disadvantages of APG

  • APG classification is restricted at taxonomic levels of only order and family. APG classification has few followers in practice.

Types of Taxonomy

1. Alpha Taxonomy

Alpha Taxonomy is the first and most basic step in the taxonomy. Alpha Taxonomy the organisms are identified, characterized, classified, and named. The pioneer or exploratory phase of taxonomy is basically analytical. It includes the collection of plants for analysis of their characters.

2. Omega Taxonomy

Also known as beta taxonomy. Omega taxonomy referred to as the experimental or biosystematics phase. It was then realized that knowing all aspects of the biology & chemistry of plants would be given a much better understanding of the relationship.

3. Gamma Taxonomy

In gamma taxonomy, we study evolutionary processes and patterns.

4. Chemotaxonomy

The chemotaxonomy uses chemical information as the character for taxonomic purposes. The chemotaxonomy gives importance to the chemical character because the chemical character is not easily changeable, these characters are stable and unambiguous.

Chemical Characters show chemical relationships amongst plants in the same way as morphological characters show morphological relationships.

5. Cytotaxonomy

In Cytotaxonomy, use of chromosome number, morphology, ploidy level, ploidy type, and chromosome aberrations as data for classification. Due to this relative conservativeness chromosome number become an important and frequently used taxonomic character.

Cytogenetics, include those studies dealing with the observation of chromosomes pairing or behavior at meiosis.

The centromere or constriction in the length of the chromosomes provides information about the relationship of the 2 arms of the chromosomes. Metacentric chromosomes are considered to more advanced than acrocentric chromosomes. The appearance of the basic chromosome set is dividing cell is known as the karyotype of the cell. This can be analyzed to provide information not only about the chromosome number but also about the chromosome size, chromosome volume, and type of chromosome in the cell. This information is used by taxonomists for identifying plants and understanding relationships.

6. Palynology

In Palynology, the study of pollen and spores.  The taxonomic characters of pollen grains include well structure, polarity, symmetry shape, and grain size.

In angiosperms pollen grains are of two types

(a) Monocolpate

(b) Tricolpate

The monocolpate pollen grain is boat-shaped, has one long germinal furrow and one germinal aperture. These is characteristics of primitive dicotyledons, such as Piperaceae and Chloranthaceae majority of monocotyledons, cycads, and seed ferms.

7. Embryology

Embryology study of the successive stages of sporogenesis, gametogenesis, and growth and development of the embryo, endosome, and seed coat. Embryological shreds of evidence have been used in solving taxonomical problems at almost all levels and have been helped resolve the doubtful systematic position of several taxa.

8. Numerical Taxonomy

Numerical Taxonomy is a classification system. Numerical taxonomy is developed for multivariate analysis. Multivariate analysis is based on the principle of multivariate statistics, which involves observation and analysis of more than one statistical outcome variable at a time. Classify organisms based on one character but always looking lots of characters during a classification at the same time. (using computer) also called Operational Taxonomic Units(OTU). A  Numerical taxonomy aims to create a taxonomy using a mathematical formula based (algorithms) like cluster analysis rather than using subjective evaluation of their properties.

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