The Plant Kingdom contains multicellular eukaryotes with the Photoautotrophic mode of nutrition.
Linnaeus gave an artificial system of classification in which plants are classified on the basis of gross superficial characters like habitat, leaves (color, shape, and number), number and shape of androecium.
The Artifical system of classification is not able to show the natural affinity between two species. As two close species may differ in morphological characters due to the effect of the environment.
Then the Natural system of classification of the system comes into action. It was given by George Bentham (1800 – 1884) and Sir Joseph Dalton Hooker (1817 – 1911).
In this along with the morphological characters, they also considered internal structures (Ultra structure, anatomy, embryology, Phytochemistry etc.). This natural system shows more affinity than the artificial system of classification.
It the branch of taxonomy that uses mathematical methods to evaluate observable similarities and differences between taxonomic groups.
Phylogenetic system of classification
It is based on evolutionary ancestry and generates trees called cladograms.
It deals with the relationships and classification of organisms using comparative studies of chromosomes.
It is based on similarities in the structure of certain compounds among the organisms being classified.
Eichler’s Classification OF Plant Kingdom
A.W.Eichler divided the plant kingdom into two groups
- Cryptogamae (Greek: Kryptos-hidden + gamos-marriage).
- Phanerogamae (Greek: Phaneros-visible or evident + gamous-marriage)
Cryptogamae plants are flowerless, seedless, fruitless plants and no visible sex organ. It is divided into three divisions- Thallophyta(Algae), Bryophyta and Pteridophyta.
Phanergamae or Spermatophyta (Sperma-seed + phyton-plants) plants have flower, seed, fruit, both seed and fruit and sex organ are visible. They have two division Gymnospermae and Angiosperms.
Engler divided the plantS into 2 groups:
- Aembryophyta (Thallophyta)
- Embryophyta (Bryophyta, Pteridophyta, Gymnosperms, and Angiosperm)
In embryophyte the zygote divide by mitosis and form embryo but in embryophytes embryo formation.
Plants in which vascular bundles are present (xylem and vessels) are known as Tracheophyta and if absent they are known as Atracheaophyta.
The study of algae is called Phycology or algology and F.E. Fritsch is known as ‘Father of algology‘
Some characteristic of algae:-
- They are Thallophyta (can’t be differentiated into root, stem, and leaf).
- Algae belong to Aembryophyta as no mitosis occurs in zygote thus no embryo form as in algae zygote divide by meiosis thus algae are haploid plants.
- They are Atracheophyta (no vascular bundles present) as most of the algae are aquatic.
- Algae are cryptogams( no flower, seed, and embryo).
- They belong to three kingdoms: Monera (prokaryotic algae, Blue-green algae), Protista (Unicellular algae, Diatoms) and Plantae (Multicellular eukaryotic algae, Spirogyra).