6. Classification of Plants.
kingdoms Monera, Protista and Fungi of the ‘Five Kingdom’ classification system proposed by Robert Whittaker (1969) for the study of living organisms.
Kingdom plantae :
- Autotrophic living organisms having eukaryotic cells with cell walls .
- Perform photosynthesis with the help of chlorophyll.
- Main source of food for all other living organisms.
- In 1883, Eichler, a botanist, classified the Kingdom Plantae into two sub kingdoms.
- Cryptogams
- Phanerogams
Basis for classification :
- Presence or absence of organs
- The presence or absence of separate conducting tissues for conduction of water and food.
- whether the seeds are enclosed in a fruit or not.
- Finally, plants are grouped depending upon the number of cotyledons in the seeds.
At the higher levels of plant classification :
- Absence or presence of flowers, fruits and seeds, plants are classified as cryptogams or phanerogams.
- Depending upon whether seeds are enclosed within a fruit or not, phanerogams are classified as -
- Gymnosperms
- Angiosperms.
- Angiosperms are further classified as -
- Monocots
- Dicots
Cryptogams :
- It Has Three Divisions
- Division I - Thallophyta
- Division II - Bryophyta
- Division III- Pteridophyta
Division I - Thallophyta:
- Grow mainly in water.
- Do not have specific parts like root-stem-leaves-flowers but are autotrophic due to the presence of chlorophyll, is called algae.
- Algae show great diversity.
- Unicellular or multicellular, and microscopic or large.
- Examples of algae are Spirogyra, Ulothrix, Ulva, Sargassum, etc.
- Some of these are found in fresh water while some are found in saline water.
- Have a soft and fibre-like body.
Division II - Bryophyta
- Amphibians’ of the plant kingdom.
- Grow in moist soil but need water for reproduction.
- These plants are thalloid, multicellular and autotrophic.
- Reproduce by spore formation.
- The structure of the plant body of bryophytes is flat, ribbon-like long, without true roots, stem and leaves.
- Instead, they have stem-like or leaf-like parts and root-like rhizoids.
- Do not have specific tissues for conduction of food and water.
- Examples are Moss (Funaria), Marchantia, Anthoceros, Riccia, etc
Division III- Pteridophyta :
- Plants from this group have well developed roots, stem and leaves.
- Separate tissues for conduction of food and water.
- Do not bear flowers and fruits.
- Reproduce with the help of spores formed along the back or posterior surface of their leaves.
- Examples are ferns like Nephrolepis, Marsilea, Pteris, Adiantum, Equisetum, Selaginella, Lycopodium, etc.
- Reproduce asexually by spore-formation and sexually by zygote formation.
- All these plants reproduce by spore formation.
- They are called cryptogams as their reproductive organs cannot be seen. (cryptos: hidden, gams: reproductive organs)
Phanerogams :
- Plants which have special structures for reproduction and produce seeds are called phanerogams.
- Seeds are formed which contain the embryo and stored food.
- During germination of the seed, the stored food is used for the initial growth of the embryo.
- Depending upon whether seeds are enclosed in a fruit or not, phanerogams are classified into
- Gymnosperms
- Angiosperms.
Division I - (Gymnosperms) :
- Gymnosperms are mostly evergreen, perennial and woody.
- Their stems are without branches.
- The leaves form a crown.
- Bear male and female flowers on different sporophylls of the same plant.
- Seeds of these plants do not have natural coverings, i.e. these plants do not form fruits and are therefore called gymnosperms. (gymnos: naked, sperms: seeds).
- The flowers these plants bear are their reproductive organs.
- Flowers develop into fruits and seeds are formed within fruits.
- Thus, these seeds are covered; hence, they are called angiosperms (angios: cover, sperms: seeds).
- The plants whose seeds can be divided into two equal halves or dicotyledons are called dicotyledonous plants.
- Those whose seeds cannot be divided into equal parts are called monocotyledonous plants.
