Leaf

Leaf is a lateral dissimilar appendage of a plant body which arises on the node of stem and bears axillary bud on its axil. It is thin flattened expanded portion considered as the site of photosynthesis. In angiosperm different types of leaves are present such as; cotyledonary leaves, bract leaves, scale leaves etc. The common type of green leaf is known as foliage leaf which consists of three major parts:

• Leaf base
• Leaf stalk or petiole
• Leaf lamina or leaf blade

Leaf base

The point of attachment of leaf with the node of the stem is known as leaf base. Sometimes the leaf base may become swollen and is known as pulvinus leaf base. Eg; Mimosa pudica(Touch me not). Sometimes in monocotyledons, the leaf base becomes expanded and winged which partially or completely covers the internode and is known as sheathing leaf base or leaf sheath.

A pair of small leaf-like structures are known as stipules may occur on either side of leaf base. Leaf with stipules is known as stipulate leaf and without stipules is known as the ex-stipulate leaf. Stipules may be of different types such as;

• linear stipules
• Ochreate
• Foliaceous

Leaf stalk or petiole

The petiole is cylindrical or subcylindrical solid or hollow stalk of the leaf which joins leaf base with the leaf lamina. Leaf with petiole is known as petiolate leaf and without petiole is known as a sessile leaf.

Leaf lamina or leaf blade

The expanded green portion of the leaf is known as leaf lamina or leaf blade which bears midrib, veins, and veinlets. Mid-rib is the main vein arising from the tip of petiole which is known as costus and its number may vary in different cases. If the upper or ventral surface of leaf differs from the lower or dorsal surface than the leaf is known as a dorsiventral leaf which is present in dicots. If the two surfaces are almost same then it is known as an oblilateral leaf which is present in monocots.

Venation of leaf