Question

As per Eichler, what are the two sub-kingdoms of the plant kingdom?

Answer 1

Biological classification is the scientific procedure to classify the organisms into different groups on the basis of their similarities and dissimilarities and placing the groups in a hierarchy of categories. Since the start of civilization many attempts have been made to classify the organisms. The criteria of classification used at that time did not fit in the scientific approach.

Complete answer:
The earlier systems of classification of organisms were simple and based on one or two characters.
First scientific attempt for classification was performed by Aristotle. He used simple morphological characters to classify plants into herbs, shrubs and trees. He also classified animals into Anaima and Enaima on the basis of absence or presence of RBCs.
Linnaeus classified all living organisms into two kingdoms- Plantae and Animalia. The criteria for classification used by him include cell wall, locomotion, mode of nutrition, response to external stimuli and contractile vacuole.
But the two kingdom classification did not differentiate between a lot of features like, the unicellular and multicellular organisms, eukaryotic and prokaryotic organisms and photosynthetic and non-photosynthetic organisms. There are few organisms like Chlamydomonas, Euglena and the slime moulds which share the characteristics of both plants and animals.
R.H. Whittaker proposed five kingdom classifications. He divided organisms into the kingdom Monera, Protista, Fungi, Plantae and Animalia on the basis of cell structure, thallus organization, mode of nutrition, reproduction, and phylogeny.
There are three main types of classifications in the plant kingdom:
(i) Artificial System of classification: It was given by Aristotle and Linnaeus and they classified the plants on the basis of vegetative characters or on the androecium structure. But they separated the closely related species.
(ii) Natural System of classification: It was given by Bentham and Hooker and they classified on the basis of natural affinities and consider not only external but also internal features like anatomy, embryology and phytochemistry.
(iii) Phylogenetic System of classification: It was proposed by Hutchinson and Takhtajan. They are classified on the basis of the evolutionary relationship of the organism.

There is another classification in the plant kingdom that differentiates between two phyla. This subdivision was given by Eichler and he used the basis of the presence of flowers and seeds. He sub-divided the kingdom into Cryptogamae i.e. the plants which lack flowers and seeds and Phanerogamae i.e., the plants that bear flowers and seeds.

Note:
Six kingdom classification was proposed by Carl Woese. He divided the kingdom Monera and Archaebacteria and Eubacteria on the basis of absence or presence of peptidoglycan in the cell wall and occurrence of branched chain lipids in the membrane and also on the sequence of 16S ribosomal RNA genes.