Leaf

Leaves are lateral appendages borne on stem. They are the photosynthetic organs of a plant. They are green in colour due to the presence of chlorophyll pigment. Each leaf possesses a bud in its axil. This Axilliary bud later develops into branches.

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Parts of a plant

Leaf Base:

  • The point where leaf attaches to the stem is called leaf base.
  • In monocots, the leaf base forms a sheath like structure encircling the stem.
  • In dicots, leaf base bears stipules.
  • If the leaf base is swollen (as in members of bean family), it is called pulvinous base or pulvinate.

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Stipules

  • These are small outgrowths seen at the leaf base.
  • Leaf with stipule is known as stipulate. When stipules are absent, the leaves are called exstipulate.

Petiole

  • The stalk of the leaf is called a petiole.
  • Leaves which do not have petiole are called petiolate, and which do not have petioles are called sessile.

Lamina / Leaf blade

  • It is the green expanded part of the leaf.

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  • Veins and veinlets are seen on the surface of the leaves.
  • The main vein is called midrib.
  • Veins provide rigidity to the leaf blade and act as channels of transport for water, minerals and food materials.
  • The tip of the leaf is called leaf apex.
  • Edge of the lamina is known as leaf margin.
  • The upper side of the lamina is called ventral side or adaxial side.
  • The lower side is known as dorsal side or abaxial side.

Types of Leaves

There are 2 types of leaves.

Simple Leaves: If a single lamina is attached to the petiole, it is called a simple leaf. (e.g. Hibiscus)

Compound leaves: If two or more lamina is attached to the petiole, it is called a compound leaf. Lamina of compound leaves is called leaflets. The main petiole is called rachis. There are two types of compound leaves: Pinnately and Palmately compound leaves.

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Pinnately compound

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Palmately compound

  • Pinnately compound leaves: The leaflets are arranged along the two margins of the rachis.
  • Palmately compound leaves: The leaflets are attached at the tip of the rachis like fingers on a palm.

Leaf Venation

The arrangement of veins on the lamina is called venation. The main vein is called the midrib. There are two types of venation.

  • Reticulate venation: The veins are branched repeatedly forming a net-like appearance. It is characteristically found in dicot plants.
  • Parallel venation: The branchlets of the veins are running parallel to one another. It is found in monocot plants.

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Banana Hibiscus

 

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