Classification

The arrangement of plants into groups and sub-groups on the basis of similarities is called classification. The characters which are uses as basis of classification are called criteria of classification. The major criteria of classification are morphology, anatomy, Palynology (study of pollen grains), Karyo logy (chromosome study), Embryology, Serology (chemical studies). Phytogeography (distribution), Paleontology and life histories. The criteria of classification are based on various field of study. It has been changed many times. Criteria depend on new investigation. For example, earlier the criteria thr classification of algae were unicellularrity or simple multicellularity and presence of pigments. Therefore, blue green algae (cyanobacteria) were placed in algae. But after the discovery of electron microscope, this criterion was changed. Now all algae were taken as eukaryotes. As cyanobacteria are prokaryotic, so they were removed from algae and placed in Monera. Many changes in criteria have occurred during whole history of the classification.

Units of Classification

The units of classificatimkare called texa. Each taxa or category is more general than the taxa or category below it. The members of lower category resemble more with one another than the higher taxon. Initially, this classification was based on appearance or morphology. Later, there was advancement in the knowledge of cytology, physiology, genetics and molecular biology. So the classification of the organisms has been modified.

Following units ofclassification are used in biology:

  1. Species: Species is the basic unit of classification. A species is a group of natural population which can interbreed freely among them and produce fertile offspring, but are reproductively isolated from all other such groups in nature. For eXample all the potato plants belong to single specie called Solarium tubersum. However, species formation by Inbreeding cannot be applied to asexually reproducing organisms. Each species has its own distinct structural, behavioural charactuistics. Different species do not exchange genes between them. So specie is an independent unit from the evolutionary unit:

  2. Genera: Genera are composed of one or more similar species. For example, Solanum tubersum, Solanutn nigrum (inako) and Solanum melangena (Bliaigan) are placed in single genera Solanum.

  3. Families: Similar genera form a family. The genus Solanum, Lycopersicum (tomato), and Nicotiana (tobacco) have common characteristics. So they are placed in single family Solanaceae.

  4. Order: Similar families form an order.

  5. Class: Similar orders form a class. For examples, all the orders of flowering plants are placed in single class Angiospermae.

  6. Phylum or division: Similar class form phylum. Phylum is also called division in plants like algae and fungi.

  7. Kingdom: Similar phyla form a kingdom. There are two kingdoms: Animal kingdom and plant kingdom

Importance of Classification

Classification has great importance for botany and botanists.

1. Classification arranges the plants in different systematic groups. It makes easy for the botanists or taxonomist to study different plants.

  1. Classification gives phylogenetic relationships among the plants. Thus evokition of plants can be studied from classification.

  2. Different members in taxonomic groups have similar characters. Thus the study of morphology, anatomy and cytology of one member gives the idea of structure of other members.

  3. Classification also gives the Phytogeography of plants.

History of Classification

  1. Pre-Linnaeus Period: Organized plant classification system was absent in pre- Linnaeus period. The Greeks classified plants on the basis of habits or economic importance. So their system is called Herbalist classification system. Some of the Greek taxonomists were Theophrastus (370-287 BC), Pliny the Elder (23-79 A.D.) Dioscorides (1° century A.D.) Magnus ( I 193- 11_1.80). Bauhin (1541-1631), John Ray (1628-1705).


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  2. Carious Linnaeus (1707-1778): Carolus Linnaeus is regarded as the father of taxonomy. He introduced first classification system. This system is considered as the beginning point. He also introduced Binomial Nomenclature. His system of classification was artificial.

  3. Bernard de Jussieu (1699-1777) and Laurent de Jussieu: They tried to .improve the system of classification of Linnaeus. They introduced the natural system of classification.

  4. Augustine Pyrame de Condolle (1718-1841): He tried to improve the classification system of Jussieu. He divided the plants into 213 orders. According to him physiological characters were useless for classification. Therefore, he used only morphological characteristics for classification.

  5. Robert Brown (1773-1849): He differentiated between angiosperm and gymnosperm plants. He also discovered nucleus in cell.

  6. Bentham and Hooker (1817- 1911): They were British Botanists. They gave their own classification system.

  7. Charles Darwin (1809 — 1882): He presented • his theory of natural selection. It introduced concept of evolution in classification.

  8. Wilhelm .Hofmeister (1824-1877): He discovered the phenomenon of alternation of generation in the lower plants. It helped in classification.

  9. Wilhelm Eichler (1839-1887): Ile introduced phylogenetic

trend in plant classification. .

  1. Adolph Engler and Karl Prantle (1849 -1893): ‘Flick system of classification was based on phylogenetic consideration.

  2. Charles Edwin Bessay: (1845 — 1915): He modified the Bentham and Hookers classification system and made this system phylogenetic.

  1. Robert Whitaker (1969): lie introduced five kingdom system. He removed algae, bacteria, and fungi from plants.

  2. Margulis and Schwartz (1988): They modified the criteria of classification of five kingdom system.

Systems of Classification

There are four systems of classification. These systems are:

1. Artificial system: The classification system based on one or two morphological characters for the identification of plants is called artificial system. This system groups many unrelated plants. Linnaeus system of classification is an example of artificial classification system.

  1. Natural system: The classification system which is based on set of charac:eristics for grouping similar plants is called natural system of classification. Various plants are grouped purely on the basis of morphological similarities in this system. Evolutionary relations are not developed in this system. The classification system of Bentham and Hooker is example of natural system.

  2. Phylogenetic system: The classification system which grouped plants on the basis of set of morphological characteristics and phylogenetic relations is called phylogenetic system of classification. The classification system of Engler and Prantle and classification system of Bessey are example of phylogenetic system..

  3. Modern System: The classification system in which plants are grouped on the basis of morphological characters and modern studies like anatomy, Palynology, serology, Karyology and embryology, Phytogeography and paleontology is modern classification system. The Takhtajans classification system is an example of the modern system of classification.

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