To endeavour to arrange plants into groups and subdivisions is called classification. Now we have subdivision of biology known as Taxonomy, which deals with principles of classification. The branch of botany in which taxonomy is of principal interest is called systematic botany.
Systems of classification: There are two systems of classification i.e. Artificial and natural.
(1) Artificial System:
The plants are classified on the basis of one or few characters which do not throw any light on the affinities or relationships of plants with one another. This results in closely related plants being placed in different groups and quite different plants in the same group because of the presence or absence of a particular only in finding out the name of a plant but gives no indication to its relationships or affinities with other plants.
Carolus Linnaens (1707 - 1778) a Swedish botanist published artificial system (1735 - 37) based on floral characters, the stamens and intersection of floral parts, hopogyny, perigyny. Epigyny being given particular importance. Linnaeus realized the imperfection of his system and regarded it as a temporary makeshift until a more natural system could be devised. This he began but did not live to complete.
His system any how supplied a pressing want and was generally welcomed by systematists as it fulfilled the immediate need of forming a complete ready made reference book for the identification of plants. His species plant arum (1753) describing all species known at the time and his Genera plant arum (1754) similarly describing the genera, stand today as the greatest of botanical classics. These works with his successful application of binomial nomenclature and his clear cut conception of species has made his name in mortal. Linnaeus divided plants into twenty classes based on the number or some other obvious characteristics of the stamens.
(2) Natural System:
This system is based not only on the characters of the reproductive organs and structural relationship but all the other important characters are also taken into consideration and the plants are classified on the basis of their related characters. It helps us not only to ascertain the name of plants but also its relationships and affinities with other plants. All the modern system of classification is natural. Linnaeus (1773) proposed a natural system but did not live to complete it. But it was adopted and improved upon by Professor Bernard de Jussulieu in France and later published by his nephew Antonie Laurent de Jassuieu (1789) in a much improved form. This was the first complete system which could claim to be a natural one. He divided plants into following groups:
1. Acotyledons
2. Monocotyledons
Benthem and Hooker:
George Benthem (1830 – 1884) and Sir Joseph Hooker (1817 – 1911) two great English systematists associated with Royal Botanical Gardens at kew, adopted very comprehensive system of classification in their “Genera plant arum” which for some years dominated the botanical world.
According to this system of classification the plant kingdom comprises about 97205 species of seeded plants included in 200 orders (or families is now understood) and grouped into cohorts (or orders, as now understood).
Benthem and Hooker system may be summarised as:
Group I. Angiosperm: Ovules enclosed in an ovary. Pollination takes place through receptive stigma and style.
Sub group A. Dicotyledons (Exogenes): Herbs, shrubs or trees of most varied habits. Stem, when peremial consisting of central pith, concentric layer of wood and a separable bark, increasing in size and thickness by means of cambium. Leaves net veined (reticulate) floral parts free or united usually in fives or some multiples of these number ovules enclosed in an ovary. Embryo with two cotyledons, radical forms the primary root.
Division I Polypetalae: Calyx and Corolla present, petals tree.
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