3. Kingdom Plantae
Kingdom Plantae is further classified on the basis of characteristics like absence or presence of seeds, vascular tissues, differentiation of plant body, etc.
Kingdom Plantae comprises multicellular, photosynthetic organisms considered as primary producers of the biosphere. They may be aquatic, terrestrial, or may even occupy other habitats. They comprise hundreds to thousands of different species. Owing to this vast diversity and number of species, various classification systems have been formulated from time to time.
For example, Linnaeus (1754) divided the Plant Kingdom into 25 classes based on the number of stamens and carpels, their union, and their presence or absence in a flower, etc.
Linnaeus' system was wholly artificial, based on the sexual characters of plants.
Artificial systems separated closely related species since they were based on a few characteristics. Also, the artificial systems gave equal weightage to vegetative and sexual characteristics; this is not acceptable since we know that often the vegetative characters are more easily affected by the environment.
As opposed to this, natural classification systems were based on natural affinities among the organisms and consider not only the external features but also internal features like ultrastructure, anatomy, embryology, and phytochemistry. Such a classification for flowering plants was given by George Bentham and Joseph Dalton Hooker.
At present, phylogenetic classification systems based on evolutionary relationships between the various organisms are acceptable. This assumes that organisms belonging to the same taxa have a common ancestor.
Numerical taxonomy is now easily carried out using computers and is based on all observable characteristics. Numbers and codes are assigned to all the characters, and the data are then processed. In this way, each character is given equal importance, and at the same time, hundreds of characters can be considered.
Cytotaxonomy is based on cytological information like chromosome number, structure, and behavior.
Chemotaxonomy uses the chemical constituents of the plant to resolve confusions and is also used by taxonomists these days.
The Plant kingdom is classified based on phylogeny and inter-relationships into Cryptogamae and Phanerogamae.
• Phanerogams
They are commonly called seed producing plants. They produce special reproductive structures that are visible (Phaneros- visible)
• Cryptogams
They are spore producing plants and do not produce seeds and flowers.
They reproduce sexually by gametes but sex organs are concealed (kryptos : hidden, gamos : marriage).
Classification of Kingdom Plantae
It is represented as follows:
