Members of the plant kingdom are called Plantae. Plant kingdom mainly comprises of eukaryotic organisms which can produce their own food by the process of photosynthesis.
Photosynthesis: This is the process by which plants use energy from the sun to convert water and carbon dioxide into sugar and release oxygen into the atmosphere.
Plant kingdom is classified based on some criteria. Features forming the basis of classification are elucidated.
• Plants having distinct parts like stem, roots and leaves.
• Plant parts have tissues to transport food and water.
• Plants bearing enclosed seeds or naked seeds.
Classification of plant kingdom
Eichler classified the plant kingdom into two sub-kingdoms - Cryptogamae and Phanerogamae.
Cryptogamae: This sub-kingdom includes plants with hidden reproductive organs and plants do not bear flowers or seeds. Cryptogams are further divided into three groups: Thallophyta, Bryophyta and Pteridophyta.
• Thallophyta are the simplest of plants that do not have a well-differentiated body design. e.g. Algae do not have leaves, stems or roots.
• Bryophyta are often called amphibians of the plant kingdom as they require both aquatic and terrestrial conditions for the completion of their life cycle. e.g. Moss or Funaria belongs to the group Bryophyta.
• Pteridophyta include fern plants which possess the plant body differentiated into stem, leaves and roots. They also possess naked embryos in the form of spores underneath the leaf.
Phanerogamae: This sub-kingdom includes plants that develop seeds and have well-formed stem, leaves and roots. Phanerogams are further classified into Gymnosperms and Angiosperms.
• Gymnosperms were the first plants to have a seed habit. These are the plants which possess naked seeds. e.g. Pinus, cycas and other coniferous trees are gymnosperms.
• Angiosperms are highly evolved plants with flowers, fruits and seeds. They are also called as flowering plants. These plants possess seeds enclosed inside the fruit. The seed germinates develops into a new plant. Angiosperms are divided into two groups, namely, monocots and dicots based on the number of cotyledons that they have.
Differences between monocots and dicots plants: These include the variation in seed, root and in leaves.
• Monocots are the plants whose seed possesses single cotyledon while dicots are the plants which possess seeds with two cotyledons. Cotyledons are also called as seed leaves. Cotyledons supply food to the growing embryos, when the seeds germinate.
• The leaves in monocot plants exhibit parallel venation while that of dicot plants include reticulate venation.
• In monocots, the primary root perishes quite early and gets replaced by a cluster of adventitious roots, while in dicots, the primary root becomes the most prominent root of the plant. This is called as the tap root, from which several lateral roots branch out.