A typical plant leaf (Different parts and types)

A typical leaf
  • The leaf is a flattened lateral out-growth of the stem/ branch and bears a bud in its axil.
  • It is green in color due to the presence of chlorophyll and constitutes the main photosynthetic organ of the plants.
  • They develop acropetally and exogenously.
  • A typical angiospermic leaf consists of three parts, namely;
    • A leaf base
    • A petiole
    • A lamina

1. Leaf base:

  • It attaches the leaf with the stem or branch.
  • In monocotyledons, the leaf base expands into a sheath that partially or wholly covers the stem while in many dicotyledonous plants it bears two lateral out growths called the stipules.
  • Depending on the presence or absence of stipules, a leaf may be stipulate or exstipulate.
  • In many plants, the leaf base is swollen and is termed pulvinus.
  • Stipules vary in form and may be of the following types:
                                                 Types of leaf bases (stipules)

a. Free lateral: Free lateral stipules are small and greenish outgrowths one on either side of the leaf base. E.g. China rose

b. Foliaceous: When the stipules are large, green and leaf like in structure, they are known as foliaceous. E.g. Sweat pea and pea

c. Adnate: The two stipules adhere to the petiole to a certain height and the structure is wing like in appearance. E.g. Rose

d. Ochreate: Here the stipules form a tubular structure covering the stem above the node. E.g. Polygonum

2. Lamina:

  • It is green, expanded portion of the leaf and is traversed by a number of veins and veinlets.
  • There is usually a middle prominent vein which is known as the midrib.
  • Veins provide rigidity to the lamina and act as channels of transport of the food materials in and out of the leaf.
  • The shape of the lamina varies from plant to plant which may be of the following types:
                                                    Shapes of lamina

a. Linear: When it is long, narrow and flat as in grasses.

b. Lanceolate: When it is lance-shaped as in bamboo.

c. Oblong: When it is wide and long as in banana.

d. Ovate: When it is broader at the base and narrower at the apex as in China rose, banyan.

e. Cordate: When it is heart-shaped as in Netel.

3. Leaf apex:

  • The tip of the lamina is described as apex which is of several types as follows:
                                                      Types of leaf apex

a. Acute: When it is pointed but not stiff. E.g. China rose

b. Cuspidate: When it is pointed, hard, stiff and spiny structure. E.g. Date-palm

c. Obtuse: When it is rounded. E.g. Banyan

d. Acuminate: When it is long and tapering. E.g. Peepall

e. Emerginate: When there is a deep notch, bifurcating the tip. E.g. Bauhinia

4. Margin:

  • The margin or the outline of the lamina is quite variable, such as:
                                                Variations in leaf margin

a. Entire: When it is even and smooth. E.g. Mango

b. Wavy: When the outline although smooth, is wavy. E.g. Ashok tree (Polyalthia)

c. Serrate: When the margin is like the teeth of a saw. E.g. China rose

5. Venation:

  • The arrangement of veins in the lamina is termed as venation. It is of two types:
                                                                   Types of venation

a. Reticulate venation:

  • When the veins are irregularly distributed forming a network, it is known as reticulate venation.
  • It is a characteristic feature of the dicotyledonous plants. E.g. Peepal, China rose etc.

b. Parallel venation:

  • When the veins are parallel an don’t form a network, it is called parallel venation.
  • It is a characteristic feature of monocotyledonous plants. E.g. Canna, grasses.
  • In both the types often, a prominent mid-vein is observed. In that case, it is described as unicostate. E.g. Peepal, Mango, Canna etc.
  • There are also leaves with more than one prominent vein. It is called multicostate. E.g. Plum, Fan palms etc.

A typical plant leaf (Different parts and types)