Taxonomy classification

Taxonomy classification, Systems of classification, Natural system of classification, Bentham and Hooker Classification, Binomial nomenclature

1. R. NITHYA M. Sc., M. Phil ., (Ph. D) ASSISTANT PROFESSOR IN BIOTECHNOLOGY SRI ADI CHUNCAHNAGIRI WOMEN’S COLLEGE, CUMBUM, THENI DT, TAMIL NADU. TAXONOMY SYSTEMS OF CLASSIFICATION

2. Taxonomy Taxonomy, a branch of science that Carl Linnaeus encompasses the description (picture, sketch), identification ,  nomenclature and classification of organisms. Using morphological, behavioral, genetic and biochemical observations, taxonomists identify, describe and arrange species into classifications. The "Father of Taxonomy", Carl Linnaeus

3. Objectives of plant taxonomy Plant Taxonomy has four objectives - To know all plants on the earth with their names, affinities and ecological significance -To build up a reference system for plants for easy identification, naming and classification - To understand the facts of evolution of different plants and phylogenetic trends in the nature - To give every plant an universal name to avoid confusions in naming of plants at the international level.

4. Plant taxonomy - Plant taxonomy is the classification of plant s on the basis of certain criteria. It is also known as systematic Botany. - It is the science that finds, identifies, describes, classifies and names plants. - Systematic Botany includes identification, nomenclature and classification of plants.

5. Identification Identification is the determination of a taxon by comparing its features identical with or similar to those of known taxa .

6. Nomenclature Nomenclature is the naming and determination of the correct name of plants. Naming of plants is a matter (topic) of international importance. Hence plants have been named according to the regulations of the International code of Botanical Nomenclature (ICBN) 1978. Naming of plant is called plant nomenclature or botanical nomenclature.  

7. Binomial nomenclature Naming of plants by two words is called binomial nomenclature. The scientific name of a plant consists of two epithets (words) namely generic epithet and species epithet. It was first introduced by Linnaeus in 1753. In binomial system generic epithet comes first and is followed by the species epithet. These words are derivatives of Greek or Latin words having some meaning related to the plant.

8. Binomial nomenclature The first letter of the genus name is capitalized but that of species name is used in small letter. The binomial name is always italicized or underlined. Ex. The binomial name of mango tree is M angifera i ndica .

9. Advantages of Binomial names Binomials are universal names for plants. They are definite and precise names. The Greek and Latin epithets are internationally known. Binomials help the taxonomists to arrange plants based on their systematic relationship .

10. Classification Classification is the arrangement of different plants in a definite order. Classification involves grouping of plants. The different groups or units of classification are called Taxa . Plant Classification contain the following taxa Kingdom, Division, Class, Order, Families, Genus and Species

11. Types of classification There are many systems of classification to arrange plants in particular sequences. All these systems can be grouped into three categories. They are Artificial system Natural system Phylogenetic system

12. Artificial system In this system only few characters of plants are considered for the classification. The plants are arranged in the alphabetic order of their names. Linnaeus (1735) proposed this system of classification. This system of classification was based on the number of stamens and arrangement of stamens .

13. Artificial system

14. Natural system In this system all characters are considered and plants are arranged according to various levels of their affinities (similarities). Bentham and Hooker’s system is a good example for the natural system.

15. Phylogenetic system In this system, all characters are considered and the plants are arranged according to their evolutionary affinities . The systems proposed by Engler and Prantl (1886), Bessey (1915), Hutchinson (1926), Tippo (1942), Takhtajan (1954), Cronquist (1981) and Rolf Dahlgren (1983)

16. EVOLUTIONARY AFFINITIES

17. Bentham and Hooker’s System of Classification This system of classification is a natural system. It explains the real situation of plants on the earth. George Bentham (1800 – 1884) and Sir Joseph Dalton Hooker (1817- 1911) were the two great British botanists , working at Royal Botanic Garden, Kew.

18. They presented their natural system of classification as a 3 volume work in Latin, titled “ Genera Plantarum ” (1862 – 1883). In this system, the names and complete descriptions of about 97,205 seed plants are given. Bentham and Hookers system of classification is considered to be the best and outstanding among all natural systems.

19. Bentham and Hooker classified the seed plants ( Phanerogams ) into three major classes namely Dicotyledons Gymnosperms and Monocotyledons

20. Bentham and Hookers system of classification

21. CLASS I. DICOTYLEDONS Two cotyledons in the embryo Tap root system Leaves with reticulate venation Pentamerous or tetramerous flowers Distinct calyx and corolla Class Dicotyledons is divided into three subclasses Polypetalae Gamopetalae Monochlamydeae

22. DICOTYLEDONS

23. CLASS II. GYMNOSPERMAE Plants bear naked seeds . They are directly divided into families Gnetaceae e.g. Gnetum Coniferae e.g.Pinus Cycadaceae e.g. Cycas

24. CLASS III. MONOCOTYLEDONS - One cotyledon in the embryo - Fibrous root system. - Leaves with parallel venation - Trimerous flowers - Divided into seven series Microspermae Epigynae Coronarieae Calycineae Nudiflorae Apocarpae Glumaceae

25. MERITS OF BENTHAM AND HOOKER SYSTEM This system has been worked out after careful comparative examination of about 97,205 seed plants. It is very simple and in workable form for field identification. Seed plants are divided into classes, sub classes, series, cohorts, families, genera and species .

26. MERITS OF BENTHAM AND HOOKER SYSTEM Monocotyledons are described after Dicotyledons . - In the classification of monocotyledons , importance was given to the position of ovary and nature of perianth . - Dicotyledons are divided into three subclasses namely, Polypetalae Gamopetalae and Monochlamydeae on the basis of nature of petals .

27. MERITS OF BENTHAM AND HOOKER SYSTEM The series Disciflorae is newly introduced. Aquatic and terrestrial conditions are considered for grouping some plants. This system has been followed in England, the USA , European countries and the commonwealth countries .

28. DEMERITS OF BENTHAM AND HOOKER CLASSIFICATION No importance is given to phylogeny of plants Gymnosperms are placed between monocotyledons and Dicotyledons for c onvenience , without considering the relative affinities. Artificial characters considered here and there. - No uniformity in the arrangement of groups

29. DEMERITS OF BENTHAM AND HOOKER CLASSIFICATION Some families placed in Monochlamydeae have much affinities with those having biseriate perianth . In the classification of Monocotyledons importance is not given to all natural characters. They are divided based on position of ovary and perianth nature alone. Some families are placed along with unrelated families E.g. Family Iridaceae is closely related to Liliaceae , but it is placed along with Scitamineae .

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