27 Aug

Floral Diversity: Plant Kingdom

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• General Features:
  • Eukaryotic
  • Multicellular
  • Non-motile (Sedentary)
  • Cell walls (Cellulose)
    • Thus, the most abundant sugar on earth is cellulose.
  • Autotrophic
• In terms of plant diversity, India ranks tenth in the world and fourth in Asia. India represents nearly 11% of the world’s known floral diversity.
• Plant Kingdom is classified in various sub-categories on the basis of following features:
  • Extent of Differentiation of plants parts like stem, roots, leaves etc.
  • Presence of special tissues (Xylem and Phloem)
  • Ability to bear seeds
  • Naked Seeds and Fruits enclosed seeds
  • Ability to produce plants
• On the above grounds, plants have been classified into five divisions:

 

 

• THALLOPHYTA (DERIVED FROM THALLUS -> UNDIFFERENTIATED PLANT BODY)
  • Plants that don’t have well differentiated body design fall in this group. They are not differentiated between roots, stems and leaves. The plants in this group are commonly called algae. The plants are predominantly aquatic.
    • Please note: In Protista we have unicellular algae, and generally all multicellular algae are put in Plantae Kingdom.
  • Features: Eukaryotic, Multicellular, non-motile, cell walls made of cellulose, autotrophic.
  • E.g. Spirogyra, Ulothrix, Cladophora, Ulva, Chara etc.
• Usefulness of Thallophyta in our life:
  • Seaweeds can be used for food purpose (soup made of sea weeds is popular in Korea and Japan)
  • Production of Biofuels
  • Anti-biotics development
  • Gellies that we get in icecreams and other sweets are extracted from an organism called Gelatin which is a Thallophyta.
• Harmful Algae’s:
  • Karenia Brevis is an alga which produces toxin and is harmful for aquatic life.
  • Eutrophication (algal bloom)

 

• BRYOPHYTES (BRYON -> MOSS; PHYTON -> PLANT)
  • They are part of Bryophyta division of Kingdom Plantae.
  • Have well differentiated body parts like stems and leaves.
  • However, no specialized tissue for conduction of waters and other substances from one part of the plant body to another.
  • Reproduction through Spores (not seeds). All Bryophytes reproduce through spores and not seeds.
  • E.g. Moss (Funaria), Marchantia, Liverworts, Hornworts, Mosses)

Mosses	Liver Worts

• • They cannot circulate rainwater through their stems and leaves but must absorb it from environment that surrounds them. Therefore, they would be found in moist environments and not dry conditions. The plant body is differentiated into a small stem and simple leaves, but true roots are absent.
  • Note: Ally Bryophytes reproduce through spores and not seeds.
  • Bryophytes are the second largest group of green plants in India distributed largely in Eastern Himalaya, North-Eastern India, Western Himalaya and the Western Ghats.
  • Mosses consist of the major component of Indian bryo flora followed by liverworts and hornworts.

 

• PTERIDOPHYTE (PTERIS -> FERNS; PHYTONS -> PLANT)
  • They are the most basic vascular plants – having simple reproductive system lacking flowers and seeds.
    • Vascular Plants: Have specialized tissues for conduction of water and other substances from one part of the plant body to another. (Xylem and phloem).
  • Well Differentiated body parts: Well differentiated plant body into roots, stem and leaves.
  • Reproduction through Spores. Produce neither flowers nor seeds, so they are referred to as Cryptogams.
  • Most of them are terrestrial plants flourishing well in moist and shady places (thus avoiding sunlight), and some of them are aquatic. This group include vascular cryptogams like club-mosses, horse-tails and ferns which are universally distributed all over the world.

Club Moss	Lady fern	Horsetail

• Note: About 1/3rd of the Pteridophytes are epiphytes (i.e., they grow on other plants).
• Note: Thallophyte, Bryophytes and Pteridophytes are called Cryptogams. This is because they have hidden (Crypto) reproductive organs. These plants are flowerless and seedless.
• In India, the north-eastern region (including eastern Himalaya) is rich in pteridophytes diversity, followed by south India (including eastern and western Ghats) and north India (including western Himalayas.
  • Note: The Thallophytes, the bryophytes and the pteridophytes have naked embryos that are called spores. The reproductive organs in all these three groups are very inconspicuous and they are therefore called ‘cryptogamae’ or those with hidden reproductive organs

 

• SPERMATOPHYTES (DISPERSED BY SEEDS)

 

A) GYMNOSPERMS (SEEDS NOT ENCLOSED) E.G., CONIFERS

• • • Group of seed producing plants that include conifers, cycads, Ginkgo and Gnetales. (Origin of word: Greek, gymnos: naked, sperma: seed). This is named so after the unenclosed condition of their seeds. The naked condition of seeds of gymnosperm stands in contrast to the seeds and ovules of flowering plants (angiosperms), which are enclosed within an ovary. In Gymnosperms ovules are present on the surface of the megasporophylls and are directly pollinated by the pollen grains. There is nothing like ovary, style, and stigma, and naturally there is no fruit.
    • E.g., Pines, Deodar, Cycads (look like palm tree, but they are not. Palms are angiosperms)

 

B) ANGIOSPERMS (SEED ENCLOSED) E.G. FLOWERING PLANTS

• • • The word is made from two Greek words: angio means covered, and sperma – means seed.
    • Angiosperms, the flowering plants are the most diverse group of land plants. Angiosperms are the seed producing plants like the gymnosperms and can be distinguished from the gymnosperms by characteristics including flowers, endosperm within the seeds, and the production of fruits that contain the seed.
    • These are the most highly developed plants which bear flowers having conspicuous accessory and essential whorls.
    • Carpels have the ovary, style and stigma. With the stimulus of fertilization the ovary generally develops into fruit and the ovules in seeds. Thus, the seed remains within the fruit.
    • Plant embryos in seeds have structure called cotyledons. Cotyledons are called ‘seed leaves‘ because in many instances they emerge and become green when the seed germinates.
      • Thus, cotyledons represent a bit of pre-designed plant in the seed.
    • The angiosperms are divided into two groups on the basis of number of cotyledons present in the seed.
      • Monocotyledons/ monocots: Plants with seeds having a single cotyledon (embryonic leaf). They are generally grass and grass-like flowering plants. (E.g. wheat, rice maize etc are a monocotyledons). Other economically important monocotyledons include Palms, Bananas, gingers, turmeric, onion, garlic etc.
      • Dicots: Plants with seeds having two cotyledons are called dicots.

• • • • India has more than 7% of the world’s known flowering plants

2) SUMMARY CHART: CLASSIFICATION OF PLANTS