Leaf in plant

Morphology of leaves deals with the study of the structural features and parts of a leaf.

The leaf is a lateral, generally flattened structure borne on the stem. It develops at the node and bears a bud in its axil. The axillary bud later becomes a branch. Leaves originate from shoot apical meristems and are arranged in an acropetal order. They are the most important vegetative organs for photosynthesis.

Parts of a Leaf

Parts of a leaf

The leaf base, petiole, and lamina are the main parts of a leaf.

Leaf Base

This is the part where a leaf attaches to a stem. Leaf base has two small leaf-like structure called stipules. In plants like paddy, wheat and other monocotyledons(this leaf base is wide and masks the stem).

Petiole

Petiole is the long, thin, stalk which links the leaf blade to the stem.

Lamina

Lamina is known as leaf blade. It is mostly green, flat surface of the leaves. It consists of a small branched vein and veinlets. The vein that runs along the middle of the lamina is called midrib. Midrib divides the surface of the lamina into two. These veins and veinlets give rigidity to the leaf blade and help in the transportation of water and other substances.

Venation

The arrangement of veins and the veinlets in the lamina of leaf is termed as venation.

Reticulate Venation

When the veinlets form a network, the venation is termed as reticulate. Leaves of dicotyledonous plants generally possess reticulate venation. Example is Leaves of rose plant

Parallel Venation

When the veins run parallel to each other within a lamina, the venation is termed as parallel. The parallel venation is the characteristic of most monocotyledons. Example is Leaves of paddy

Types of Leaves

There are two type of leaves which are further classified into different groups based on their shape, size, their arrangements on the stem, leaves of flowering and non-flowering plants, and various other physical attributes.

1. Simple Leaf

In this case, a single lamina is connected to the main stem by a petiole than leaf is said to be simple. A simple leaf may be incised to any depth but not down to the midrib or petiole, example is Guava leaves.

2. Compound Leaf

A compound leaf is a leaf made up of more than one leaflets. In a compound leaf, the midrib of the leaf is branched into different leaflets and is connected by a single petiole, examples are Pea, palm leaves.

These are further sub-divided into the following types:

Palmately Compound Leaf	Pinnately Compound Leaf

2.1 Palmately Compound Leaf

In this case, the leaflets are attached at the tip of the petiole and can be differentiated into following:

Unifoliate	The leaves have only one leaflet.	Citrus
Bifoliate	The leaves have two leaflets.	Balanites
Trifoliate	The leaves have three leaflets emerging from the same point.	Oxalis
Quadrifoliate	The leaves have four leaflets arising from the same point.	Marsilea
Multifoliate	This type of leaf has many leaflets arising at a common pint.	Bombax

2.2 Pinnately Compound Leaf

In this case, the midrib of the leaf is divided into numerous leaflets and all connected by a common axis.and these can be further differentiated into following:

Pinnate	A compound leaf that has an axis on each side of the midrib is known as a pinnate leaf.	Example
Unipinnate	The leaf with leaflets on each side of the axis.	Cassia
Bipinnate	In this case, a secondary axis bearing the leaflet is produced by the central axis.	Acacia
Tripinnate	In this case, a tertiary axis bearing leaflets emerges from the secondary axis.	Moringa
Decompound	In this case, Leaf with more than three pinnate.	Old leaves of coriander
Parapinnate	In this case, A leaf without a terminal leaflet.	Cassia
Imparipinnate	In this case, Leaf with an odd terminal leaflet.	Pea

Phyllotaxy

The leaves arrangement patterns on the stem are called Phyllotaxy. Plants show three types of phyllotaxy as follows:

Alternate	When only a single leaf develops at each node alternatively, example is China rose.
Opposite	When a pair of leaves develops at each node opposite to each other, example is Guava plants.
Whorled	When more than two leaves develop at the nodes to form a whorl of leaves, example is Alstonia.