Kingdom Plantae consists of all plants which are multicellular eukaryotes with cell walls.
All plants contain plastids. Plastids are double-membrane organelle that possesses photosynthetic pigments called chlorophyll.
They are autotrophs and use chlorophyll for photosynthesis. A few members are partially heterotrophic such as the insectivorous plants or parasites. Bladderwort and Venus fly trap are examples of insectivorous plants and Cuscuta is a parasite.
The members of Plantae are the main producers and provide food directly or indirectly to all living organisms. Reserve food material is in the form of starch.
Vascular tissues are absent in lower plants i.e. Algae and Bryophytes but present in higher plants i.e. Pteridophytes, Gymnosperms, and Angiosperms.
The life cycle of plants has two distinct phases the diploid sporophytic and the haploid gametophytic – that alternate with each other. The lengths of the haploid and diploid phases, and whether these phases are free-living or dependent on others, vary among different groups in plants. This phenomenon is called alternation of generation.
Kingdom Plantae includes algae, bryophytes, pteridophytes, gymnosperms, and angiosperms.
Levels of Classification of Plants:
There are three levels of classification among plants.
The first level of classification among plants depends on whether the plant body has well- differentiated, distinct components. Depending upon this criteria plants are classified as Thallophyta, Bryophyta, and Pteridophyta. The thallophytes, the bryophytes, and the pteridophytes have inconspicuous reproductive organs hence they are therefore called ‘cryptogamae’, or ‘those with hidden reproductive organs’.
The second level of classification is based on whether the differentiated plant body has special tissues for the transport of water (xylem) and other substances (phloem)within it. Depending upon this criteria plants are classified as vascular (having xylem and phloem) and non-vascular (not having xylem and phloem).
The next level of classification is based on seed producing and non-seed producing. If seed producing then on the basis whether the seed is enclosed or not.
In 1883, Eichler divided the kingdom Plantae into two sub-kingdoms, Cryptogamae and Phanerogamae
The plants of this group bear naked seeds and are usually perennial, evergreen and woody.
It includes medium sized trees and shrubs.
Sporangia are formed over modified leaf-like structure called sporophylls. There are two types of sporophylls. Megasporophyll bears megasporangium (ovule). It produces female gamete. Microsporophyll bears microsporangium (pollen sac). It produces male gamete.
The seeds develop inside an organ which is modified to become a fruit.
These are the highly evolved group of plants.
The reproductive organs are aggregated into flowers. The male sex organs are called stamens and female sex organs are called pistil.
Plant embryos in seeds have structures called cotyledons. Cotyledons are also called ‘seed leaves’ because in many instances they emerge and become green when the seed germinates. Cotyledons store food for developing embryo.
The angiosperms are divided into two groups on the basis of the number of cotyledons present in the seed. Plants with seeds having a single cotyledon are called monocotyledonous or monocots (e.g. Maize, rice, wheat). Plants with seeds having two cotyledons are called dicots (e.g. bengal gram, garden pea).
Class Dicotyledonae (Dicots):
They have two cotyledons in the seed.
Their leaves show reticulate venation with a network of veins.
Their root system is tap root system.
Stem is strong and hard.
The flowers have five or multiple of five petals.
Some examples are Pea, Mango, Bengal gram Banyan, etc.
Class Monocotyledonae (Monocots):
They have one cotyledon in the seed.
Their leaves show parallel venation.
Their root system is fibrous root system.
Stem may be hollow (e.g. Bamboo), False (e.g. Banana) or disc-like (e.g. Onion)
The flowers have three or multiple of three petals.
Some examples are Wheat, Rice, Maize, Sugarcane, Coconut, etc.