Morphology of Flowering Plants

Leaf


  • A leaf is green, dorsoventrally flattened, exogenous lateral outgrowth that arises from the node of the stem or its branch.
  • A typical leaf has 3 basic parts (i) Leaf base (or) Hypopodium is the point by which the leaf is attached to the stem, which is made up of stem cells.
  • Pulvinus is the swollen leaf base is legumes, which act as motor organs that is responsible for sleep movements and shock.
  • Petrole (or) mesopodium is leaf stalk that is developed is the last during leaf development. Sessile leaf is without  a petiole eg : Calotropis.
  • Lamina (or) Epipodium (or) leaf blade is the flat green photosynthetic part of leaf.
  • Caducous leaf fall off soon after their formation Eg : Opuntia.
  • Deciduous (annual) fall under unfavorable conditions (or) at the end of growing season (Eg : Mulberry, Poplar)
  • Persistent (evergreen) leaves remain on the plant for more than one year, fall of individually at different times. Eg : Eucalyptus.
  • The mode of arrangement of mature leaves on the stem orbits branches is called phyllotaxy which is of 4 types.
  • Spiral ; opposite : syzigum, calotropis, guava ; opposite (or cyclic) is of 2 types
    (i) opposite and superposed and (ii) opposite and decussate.
  • Quisqualis belong to both the opposite types.
  • Whorled or verticillate (Eg : Nerium, Alstonia, Hydrilla)
  • Leaf mosaic : Acalypha
  • Arrangement of vein and vein lets in the lamina is called venation
  • Reticulate venation forms network is dicots [Exception also in mono cots (Eg : colocosia, Alocosia)]
  • Pinnate (or) unicostate reticulate venation [eg : Peepal, mango, shoe flower] and palmate (or) Multicostate reticulate venation (Eg : Luffa, castor, zizyphus) are the 2 types of former type.
  • Parallel venation is without network, where veinlets are not conspicuous, which is found in monocots. [Exception also is dicots like calophyllum, corymbium, eryngium]
  • Unicostate parallel : Eg : Banana, canna ; palmate (or) Multicostate parallel vention : Eg : Grass, Wheat, Bamboo, Fan palm
  • Two types of leaf are (i) simple and (ii) compound
  • A leaf with undivided lamina is known as simple leaf.
  • Compound leaf is the one where the lamina is divided completely into distinct and separate segments called leaflets which don't bear leaflets.
  • Two types of compound leaf are (i) Pinnately compound and (ii) Palmately compound.
  • Unipinnate : Eg : Tamarindus, Murraya, Rose.
  • Bipinnate : Eg : Acacia, Mimosa
  • Tripinnate : Moringa
  • Decompound is the leaf more than three pinnate : Parthenium, coriander, carrot, fennel
  • Palmately compound leaf do not possess Rachis that has an appearance of palm.
    Eg : Oxalis, Marsilea, zorina, Bombax
  • The leaf has several modification which have been list out below.
  • Leaf Tendrils (Eg : Wild pea, Lathyrus odoratus, Nephenthes, clematis, glory lily)
  • Leaf spines (Eg : Opuntia, Asparagus, Barberry, Agave, Brinjal, Alove)
  • Leaf roots (Eg : Salvinia)
  • Phyllodes are flattened petioles and raches which have taken over the function of lamina as the latter is reduced Eg : Acacia, Parkinsonia.
  • Insectivorous plants grow in bags that are deficient in nitrogen, so they trap insects no bigger than butterflies and digest their proteins by extracellular digestion by enzymes like pepsin and proteases. Eg ; Nepenthes and Drosera.

View this video for the topic from 26:05 to 43:02

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