Angiosperm

biology

In Nepal: 1700+ specie of medicinal herbs and 200 species of aromatic.

  1. Angiosperms are the most advanced and highly evolved groups in flowering plants.
  2. The word Angiosperm is derived from two Greek works Angion = cover & sperma = seed.
  3. Thus, the enclosed seeded plants or plants having seeds with ovary are known as Angiosperm.
  4. It is believed that they are originated 135 million years ago in Mesozoic era (at the end of this era)
  5. There are about 2, 50,000 Angiospermic plants distributed worldwide.
  6. Plant body is perfectly sporophytic, gametophyte is reduced in the form of pollen grains (male gametes ) and ovule (female gametes)
  7. On the basis of distribution/habitat, they are categorized as below
    • Hydrophyte : Plants living in wate. E.g. Hydrila
    • Mesophyte : Plants growing in moderate supply of water (growing on land with sufficient water) Eg : mango tree
    • Xerophyte : Plats growing on desert (dry) places . E.g. Opuntia
  8. On the basis of habitat, they are categorized as below
    • Herb: sunflower, mustard etc.
    • Shrub: rose etc.
    • Tree: sal, peepal etc.
  9. On the basis of life-span, there are 3 types
    • Annuals : soyabean, grains, mustard etc.
    • Binneals: carrot, raddish, sugarcane etc.
    • Perinneals: shrubs and trees
  10. Plants bear conspicuous flower.
  11. Plants flowers are trimerous (monocots), tetramerous (mustard ) and pentamerous (Pentamerous flower contains “epicalyx” as fifth layer )
  12. The sporophyll (spore bearing part) is represented by flowers.
  13. During pollination, pollen grains are deposited on stigma of flower, pollen tube is developed and helps to transport male gametes to the ovary.
  14. Double fertilization and triple fusion is special feature in angiospermic plants.
  15. Endosperm is triploid in nature.
  16. Seed is formed inside the ovary or fruit.

    Note: Endosperm is the reserved food material for growing embryos and it is always triploid in nature in angiosperms.

  17. Angiosperm plants are broadly divided into the following groups :
    Dicotyledonous  :

    • The leaves are dorsiventrally flattened. Dorsal side has more number of stomata where as ventral side has less.The leaves are almost oval and slightly longer than width.
    • The leaves have reticulate venation.
    • There is tap root system.
    • Vascular bundles are arranged in rings.
    • Stem is more hairy.
    • Flowers are tetra to pentamorous. (eg: Chinarose, hibiscus)

    Monocotyledons:


    • The leaves are isobilateral. Number of stomata is almost the same in upper and lower parts of leaves.
    • The leaves are linear long.
    • The leaves have parallel venation.
    • There is adventitious or fibrous root system.
    • Vascular bundles are scattered.
    • Stem is less hairy.
    • Flowers are trimerous. (eg: Tradescantia, wheat, paddy etc..)
  18. Cambium – present inside the stem, which causes secondary growth of plant.
  19. Perinath – calyx + corolla = trimerous flowers
  20. Morphology :
    It is made of two Greek words: i) Morphae – form ii) Logous – Study or discourse.
    Branch of biological science dealing with the study of structure, form, size, colours, texture and relative position of parts or organs.
  21. Taxonomy is the branch of science hat deals with the classification, identification, nomenclature and description of the organism.
  22. The Root System :-
    Root is the non-green descending part of the vascular plants growing under soils. It is positively geotrophic and negatively phototrophic. Generally, it arises from radicle of the embryo of seed. Primary root which comes from radicle gives rise to secondary root, and secondary root in turn fives tertiary roots. The root system consists of primary root, secondary rot and tertiary root.
  23. Functions of Roots :-
    • Absorption of water, minerals and salt fro soil and transportation of them to stem.
    • Support to plant or anchroragement (mechanical support) to all aerial parts.
    • Storage of food and certain modified types of roots store large amount of food. Eg: radish, sweet potato, carrot etc..
  24. Types of Roots :-
    • There are two types of root, Tap root and Adventitious root.
    • Tap root always arises from radical of embryo of the seed. Tap root is persistent throughout the life.
    • The root arising from other parts except radical is known as adventitious roots. Fibrous root is one type of adventitious root.
    • Adventitious root may arise in dicots and monocots as well. Eg : In dicots (sweet potato, bar potato etc..) & In Monocots (Maize etc..)

     

  25. Modification of tap root :
    Tap root are modified into different forms as mentioned below:-

    • Conical root: This type of root is fleshly thickest at the base and gradually tapering towards apex as a cone.
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    • Fusiform root:  This is the spindle shaped i.e. thick at middle and narrow towards both ends. Eg: radish
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    • Napiform root: The root is almost spherical at the base and suddenly tapering towards apex. Eg: turnip
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    • Nodulated root: In leguminious plants, there are small or large small irregular swelling called nodules.
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    • Tuberous root: They are also fleshly, tap roots but do not assume and definite form. Eg: Mirabilis
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    • Reproductive root: Some  of the tap roots bear adventitious buds that  can grow to form new plants. Eg: Sisso
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    • Mycorrhizal root: In some plants, the root lacks root hairs and absorption is supported by a kind of fungi called mycorrhiza. This fungi has hyphue penetrated up to the inner part of root. Eg: Pinus. Association of mycorrhizal is also found in adventitious roots.
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  26. Modification of Adventitious root
    • Tuberous roots: In some horizontally prostate plants, nodes give rose to adventitious roots. These root form tubers after irregular swelling. They are known as tuberous roots. Eg. Sweet Potato
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    • Fasciculated roots: They are swollen like the tubers but are found in cluster. They arise from a common point of stem and lie at the base of the stem. Eg: Asparagus, Dahlia, etc.
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    • Palmate roots: This type of root is branched like the palm of the human hand. Eg: Some orchids
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    • Moniliform roots: These types of roots are swollen at regular intervals forming the bead like structure or necklace like structure. They are also called beaded roots. Eg: Discorea, Momordica
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Types of Adventitious Roots for mechanical support:

  1. Stilt roots: In some of the plants, the stem is long and narrow due to which normal fibrous adventitious roots are in capable of holding the stem perfectly erect. To provide support to the stem, adventitious roots arise from the few lower nodes. These roots are thick and strong, known as stilt roots. Eg: In pandanaus, Sugarcane, Maize etc..
  2. Prop roots: In some plants with large and horizontal branches, the roots are adventitiously from the large branches for mechanical support. Initially, they hang down in air and grow down ro meet the oil. After meeting the soil, they become thick and strong. Such types of roots are known as prop roots. Eg: In Banyan tree
  3. Climbling or Clinging roots: These roots originate from the nodes and attach themselves to any support near to them. Eg: In Betels, Pothos(money plant) etc..

Adventitious Roots for vital functions:

  1. Epiphytic roots: In some plants like orchids, growing on the barks of some trees, aerial roots are produced and these roots help to attach them on the trunk of big trees. These roots contain a dead spongy substance, known as Velamen. They do not draw nutrients but absorb moisture from surrounding air. Eg: Orchids
  2. Parasitic Haustoria roots: Some parasitic plants develop a sucking apparatus and penetrate to the tissue of host to absorb nutrients. This apparatus is known as parasitic roots or haustoria. Eg: In Cuscuta, Mistletoe etc.
  3. Assimilatory Roots: These roots are developed from the branches of certain plants. These roots roots are long slender, hanging and have chlorophyll that help in photosynthesis. Eg. Tinospora, Tropa etc.
  4. Respiratory Roots or Pneumatophores: These roots are developed by some plants growing in salty water or in tidal swamps. These roots grow vertically upward from the underground roots. They appear like conical spikes coming out of water. They contain well-developed air spaces communicating through pores that help in respiration. Eg: Rhizophora, Mangrove, etc.