Leaves – Morphology, Types & Modification

Leaves are the lateral appendages of the stem. The primary function of Leaves is to make glucose and produce oxygen by using sunlight, CO₂ and H₂O via the process known as photosynthesis. The structure of the leaf is composed of three parts including leaf base, lamina, and petiole. There are diverse types of Leaves present which depend upon the type of plant species. Chlorophyll is present in leaves which provides a green color and participates in photosynthesis.

What are Leaves?

Leaves are green-colored, flat, thin lateral appendages of the stem. It bears a bud in its axil which is borne at the node. It contains a photosynthetic pigment i.e. chlorophyll, so that its color is green. This photosynthetic pigment participates in the synthesis of organic food for the plant.

Morphology of Leaves

Morphology deals with the study of the structural features and parts of the organism. Morphology of the leaves is the study of the structural features and parts of the Leaves. Leaves are flat thin and green in color. These are laterally developed from the node and originate from the shoot apical meristem.

Structure of Leaves

Mainly plants have leaf bases, petioles, and lamina, all these together form the main parts of the Leaves.

• Leaf Base: The part at which the leaf attaches to the stem leaf-like is called as leaf base. It has two leaf-like structure which is called stipules.
• Petiole: It is a thin, long stalk that joins the leaf blade to the stem.
• Lamina: It is the green color flat surface of the leaf which is also known as leaf blade. The surface of the lamina is divided into two which is called midrib. Lamina also consists of small branched veins and veinlets. Veins and veinlets help in the transportation of water and minerals and also provides the rigidity to the lamina. The arrangement of veins and veinlets are known as venation. Mainly it is of two types:
  • Reticulate venation: In this type of venation, the arrangement of veinlets are random and forms a complex network. Example- Dicotyledonous plants.
  • Parallel venation: In this type of venation, the veinlets are run parallel to one another. Example: Monocotyledonous plants.

Parts of a Leaf

Types of Leaves

Mainly Leaves are of two type: Simple and Compound Leaves. These further divided on the basis of shape, size, and arrangenmnet of Leaves on stem.

Simple Leaves

When main stem is linked to the petiole through a single lamina. Example Guava leaves

Compound Leaves

When midrib is branched into many leaflets and connected through single petiole. These Leaves are divided into two sub-types: Pinnately and palmately compound Leaves.

Pinnately Compound Leaves

In this type of Leaves, midrib is divided into various leaflets and these leaflets are connected by a common axis. These are further divided into following types:

• Pinnate: In this type of Leaves, the midrib is on each side and have only single axis.
• Unipinnate: Leaflets are present on each side of the axis.
• Bipinnate: Leaflets are import from the secondary axis which are produced from the central axis.
• Tripinnate: Leaflets are import from tertiary axis which emerges from the secondary axis.
• Decompound: The leaf which have more than three pinnate.
• Parapinnate: In this type of leaflet the terminal leaflet is absent.
• Imparipinnate: The leaf which have an odd terminal leaflet.

Palmately Compound Leaves

In Palmately Compound Leaves type of Leaves, leaflet is attached to the petiole tip. These are further divided into following types:

• Unifoliate: These Leaves have single leaflet.
• Bifoliate: These consist two leaflets.
• Trifoliate: These consist three leaflets and these three leaflets are arising from single point.
• Quadrifoliate: These consist of four leaflets and all these four leaflets are arising from single point.
• Multifoliate: These leaves are consist of more than four leaflets and all leaflets are arising from same point.

Types of Leaves

Modification of Leaves

Mainly Leaves perform photosynthesis but these are also participate in different roles like storage of food, support, defence etc. To perform these functions Leaves are modified into different forms like:

• Tendrils: When Leaves are modified into wiry and structures then these are called as tendrils, these are help the climbers to climb.
• Spines: When Leaves are converted into pointed structure and these structures protect the plant from herbivores.
• Phyllode: When petiole is modified into extended green structures which carries out photosynthesis.
• Storage leaves: Due to storage of water and food these Leaves are become fleshy.
• Cotyledons: Cotyledons are shown by mature embryo which may be one or two.
• Leaf bladders: Leaves of the some aquatic plants are modified into leaf bladders which trap the small insects.
• Leaf pitcher: Leaf lamina is modified into a lid which is called as pitcher and this trap the insects and fulfill nitrogen requirement.

Modification of Leaves

Functions of Leaves

Leaves participates in many functions like:

• Photosynthesis: Leaves have green color pigment i.e. chlorophyll which entrap sunlight and forms glucose from carbon-dioxide and water. This process is called as photosynthesis.
• Transpiration: Leaves remove the excess water through stomata in the form of water vapor and allows the water conduction from the roots.
• Exchange of gases: Through stomata exchange of gases takes place.
• Storage of food: In some plants, modified Leaves are present which participate in storage of food.

What is Phyllotaxy?

Leaf arrangement on plant stem is known as phyllotaxy. It explains how Leaves are arranged and positioned in respect to one another along the stem. Phyllotactic patterns that are frequently seen include whorled, opposing, and alternating, which have two Leaves per node that are positioned exactly across from one another. Genetic and environmental variables impact phyllotaxy, which helps plants maximise light exposure and make effective use of their resources.

Key Points on Leaves

1. The photosynthetic pigment chlorophyll is present in Leaves, which are located at the stem’s nodes.
2. A leaf is composed of three primary parts: the petiole, the lamina, and the base of the leaf.
3. Simple Leaves and complex Leaves are the two different kinds of Leaves.
4. They assist in the process of removing extra water from the plant’s aerial portions and carry out photosynthesis.
5. Their ability to adapt to different settings is aided by their modification in the form of scales, tendrils, hooks, and spines.

FAQ’s – Leaves

1. What is the Important Function of Leaves ?

Important function of Leaves is that they participate in photosynthesis; during photosynthesis carbon-dioxide (CO₂), water (H₂O) and sunlight get converted into glucose and energy.

2. What consist the Structure of Leaves ?

The structure of Leaves comprises three main parts: the leaf base, petiole, and lamina. The leaf base is where the leaf connects to the stem. The petiole is a slender, elongated stalk that connects the leaf blade to the stem. The lamina, also called the leaf blade, is the flat, green surface of the leaf.

3. How many Types of Leaves are there?

Leaves are categorized into two main types: simple and compound leaves. Simple Leaves have a single lamina directly connected to the main stem through the petiole. In contrast, compound leaves have a midrib that branches into multiple leaflets, all linked through a single petiole.

4. What is Venation and its Type ?

Venation refers to the pattern of veins and veinlets in Leaves, and it can be classified into two main types. Reticulate venation is commonly found in dicotyledonous plants and other is parallel venation features in monocotyledonous plants.

5. What are the Types of Phyllotaxy ?

Phyllotaxy refers to the arrangement pattern of Leaves on a stem, and it comes in three main types.

1. In alternate phyllotaxy, leaves are arranged singly.
2. In opposite phyllotaxy, Leaves are paired at the same node.
3. The whorled type of phyllotaxy involves three or more Leaves attached at a single node.