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Leaf: Phyllotaxy & Modifications

Phyllotaxy

The mode of arrangement of leaves on the stem is known as phyllotaxy. There are three types of phyllotaxy in Angiosperms.

  1. Alternate phyllotaxy: A single leaf arises from the nodes. (e.g. Hibiscus)
  2. Opposite phyllotaxy: Leaves are arranged in pairs at each node. (e.g. Ixora)
  3. Whorled phyllotaxy: More than two leaves are arranged at each node. (e.g. Nerium)

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Leaf Modifications

The normal functions of leaf are photosynthesis, transpiration and respiration. Some leaves are modified to perform specialized functions.

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Leaf tendrils:

These are slender, wiry and coiled structures which help to climb on a solid support. (e.g. Pisum)

Leaf spine:

  • In plants living in arid area, the leaves are modified into sharp and pointed structures called spines.
  • They help in defence against enemies, and in reducing loss of water through transpiration. (e.g. Opuntia)

Leaf scale:

  • In some plants, the leaves are modified into thin membraneous structures called leaf scales.
  • In onion, these scales are fleshy due to storage of food materials.

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Phyllode:

  • In some plants, the leaflets will fall soon after formation, and the rachis is modified into flattened, swollen and green leaf like structures to carry out photosynthesis.
  • Such modifications of petioles into photosynthetic structures are known as phyllodes. (e.g. Acacia)

Pitchers and Bladders

  • In insectivorous plants, the leaves are modified into flask shaped structures called pitchers (e.g. Nepenthes) or bladder like structures (e.g. Utricularia).
  • These are used to capture and digest insects and small animals.

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Heterophylly

The presence of more than one type of leaves on the same plant is known as heterophylly. (e.g. Limnophylla heterophylla)

 

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