Flowering plants encounters the most dominant plant cover over the terrestrial world. There are about more than 300, 000 known species of flowering plants so far discovered of these angiosperms are about 200,000 species under more than 300 families and 12,500 genera. They are of diversed habitat and form.
Arrangement of these varieties of plants into groups' sub- groups divisions and other taxonomical ranking for easier understanding systematically is called as classification. The principal basis of classification is the life history reproductive structures etc.
There are two distance systems of classifications one is artificial and other is netural system.
Natural System of Classification:
Natural system of classification is based on the natural characters of the species particularly the reproductive organs and structural relationship in this system not only the reproduction feature but all other important characters of plant body has been taken into consideration. Plants are classifies according to their related characters. It not only helps to ascertain the name of a plant but also its relationship and affinities with other plants. All modern systems of classifications are natural classifications.
The natural classification was made by various taxonomists viz. Jhon ray Linnaeus, A.P. decandolle, Endlicher, Bentham and hooker, Engler and Prantl and Hutchinson of above. Hutchinson's classification is based on phylogenetic relationship among the plants besides the natural character. The classification made by Engler and Pantle is purely natural.
Engler and Prantl's classifications:
Adolph Engler and Karl prantl two German botanists published their classical treaties in "Die Naturalichen Pflanzenflamilien "in form of 23 volumes covering the entire plant kingdom in a systematic order of arrangement. They made attempts to rectify the short comings of Eichler and Bentham and hooker's classification.
Salient features of the classification:
i. Monochlamydea is completely abolished as such and famlies are distributed in the large series called Archichlamydeal.
ii. This Engler system dominates over all the natural system but not to the exclusion of other.
iii. They accept the theory of descends and threw light or the phylogeny of various groups.
iv. It traces upon the increasing complexity of plant parts particularly essential whorls of flowers.
v. Most primitive type of flowers has no perianth; in the next evolved type two who0rls of perianth then in highest evolved type there are two whorls of perianth in latter case two whorls are indistinguishable (Homochlamydous) or distinguishable (Heterochlamydous).
vi. Gamopetalous condition considered more advanced than the poly patulous condition and the monocotyledonous are primitive and place before the dicotyledonous plants.
vii. Hypogenous form of arrangement is primitive to perigyny to a definite number of stamens and carpals.
viii. Indefinite number of stamens and carpals are primitive to a definite number of stamens and carpals.
ix. Monocotyledons have been classified into 11 orders and 45 families where as Dicotyledons classified into 44 orders and 261 families.
x. Monocotyledon starts with family typical and ends in Orchidaceae.
xi. Dicotyledonae begins with family Casuarinaceae and ends in Compositae.
xii. Engler assumes that, Casuarinaceae with unisexual apetalaces flowers borne in catkins is the most primitive family among dicots.
This system is summarized as follows. All flowering plant belongs to.
Embryophyta or Siphonogamia or spermatophyte further this division sub-divided into two sub-division.
i. Sub-division -1 Gymnospermae (naked seeded)
It includes seven classes' viz. class-cycadofilicales, Cycadales, Bennetitales, Ginkgoles, Coniferales, Cordaitales and Gnetales.
ii. Sub-division: Aniospermae. This sub-division further divided into two major classes.
iii. Class -1 - Monocotyledonal (Embryo with single cotyledon) further, this class have been classified into 11 orders