Types of Leaves ( Simple and Compound leaves), Practice Problems, and FAQs

We humans are different from each other because of the differences in our DNA sequences. Although we belong to the same species, we have different fingerprints, eye colour, skin colour, height, face shape, eye shape, etc. Even within the same family, we share similarities with other family members but are never identical to them.

Similarly, when you see different types of trees near your surroundings, do you notice that all these plants have different types of leaves? Even within the same tree, the leaves having more exposure to light will be greener compared to the rest. Now you must be wondering that if all the leaves perform the same function of photosynthesis, then why do they differ so much? What determines the different shapes and sizes of leaves? 

Fig: Different types of leaves

The different shapes, sizes and colours attained by leaves are a function of their genetic composition which in turn has been influenced by the long ecological and evolutionary history of that particular plant species. The specific shape, size and type of a leaf is tailor made to adapt to the environmental conditions of the plant’s habitat such that it can show maximum efficiency in function.

Leaves can be of different types based on their leaf blades, their lifespan and their position in the plant body. In this article we will discuss the different types of leaves.

Table of contents

• Structure of a leaf
• Types of leaves
• Simple leaf
• Compound leaf
• Practice Problems
• FAQs

Structure of a leaf

In plants, photosynthesis is carried out by leaves, which are slender, flat structures that grow laterally at the nodes. Leaves develop from the shoot apical meristems and are a crucial component of the shoot system. The area of the embryo between the cotyledons, known as the SAM (Shoot apical meristems), contains meristematic cells which divide and differentiate to give rise to leaves.

Fig: Shoot apical meristem (SAM)

The shoot's apical meristematic zone keeps climbing up the shoot as it expands, eventually taking up a position just above where the last set of leaves had grown. As a result, leaves develop acropetally, that is, one by one from base to tip.

Fig: Position of shoot apical meristem

The leaf is composed of four parts that are listed below:

• Leaf base
• Stipules
• Petiole
• Lamina

Leaf base

This is the region where a leaf joins the stem. The leaf base is broad and covers the stem in plants like rice, wheat, and other monocotyledons.

Fig: Leaf base

The base of the leaf in some plants contains two tiny stipules that resemble miniature leaves. Such plants are said to be stipulate plants. 

Fig: Stipules

Petiole

The leaf lamina is joined to the stem or branch by the petiole, also known as the mesopodium, or stalk of the leaf. The leaf should be positioned for optimal light exposure. Long, thin, and flexible petioles enable the leaf blade to flap in the wind, which aids in bringing fresh air to the leaf surface. Sessile leaves are those without a petiole, whereas petiolate leaves are those with one.

Fig: Petiole of a leaf

Lamina

Lamina is also known as a leaf blade. It is the leaf's flat, green surface. It is made up of veinlets and a small branching vein. Midrib refers to the vein that runs down the centre of the lamina. The lamina's surface is split in half by the midrib. These veins and veinlets offer the leaf blade stiffness and aid in the movement of water and other materials.

Fig: Lamina

Types of leaves

Leaves can be classified into various types based on various criteria such as life span, the shape of the leaf blade and the role they perform in the plant body.

Based on life span

On the basis of life span, leaves can be classified as -

• Caducous - The leaves fall off soon after their separation and elaboration from the bud, as seen in Opuntia.

• Deciduous - The leaves remain on the plant throughout the growing season and fall off upon the approach of unfavourable season like autumn and winter, e.g., mulberry.

• Persistent - The leaves live for more than one year and through both favourable and unfavourable seasons. Such leaves are also known as evergreen leaves, e.g, Mango.

Based on their role

Based on the role played by a leaf, it can be of the following types - 

• Foliage leaves - these are the green photosynthesising leaves that are borne laterally on the nodes of the stem or branches.
• Cotyledons - these are the seed leaves which are borne over the node of the embryo axis and help in storage of food for the growing embryo.
• Scale leaves or cataphylls - these are small stalkless reduced forms of leaves which can store food, as seen in onion. Scale leaves of onion also help to protect the bud.
• Bracts - these are leaf-like structures at the axil of flowers which can help in attracting pollinators when they are large and coloured, e.g., Bougainvillaea.
• Floral leaves - These are modified leaves that are borne on the thalamus of a flower and serve as non-essential flower whorls such as petals and sepals. Petals help in attracting pollinators while the sepals help in protecting the flower at bud stage.
• Sporophylls - These are modified leaves which form the essential floral whorls, namely, androecium and gynoecium. These leaves are specialised to bear a sporangium within which sexual spores are formed.

Based on leaf lamina

Based on the leaf lamina, there are two main categories of leaves: simple and compound. Simple and compound leaves are divided into several groups according to their size, form, placement on the stem, whether they are on flowering or non-flowering plants, and various other physical characteristics.

Simple leaf

The term "simple leaf" refers to a leaf that has a single lamina and a petiole connecting it to the main stem. The lamina of simple leaves can have incisions to any depth, but they cannot be up to the midrib or petiole. Examples include guava leaves. 

Fig: Simple Leaf

Compound leaf

In compound leaf, the leaf blade is divided into two or more leaflets as the incisions of the lamina reach up to the midrib and break it into a number of leaflets. A single petiole connects the several leaflets that branch off from the midrib of a complex leaf. Examples include palm leaves, peas leaves, etc. 

Fig: Compound Leaf

The compound leaves are further divided into two categories:

• Palmately compound leaf
• Pinnately compound leaf

Palmately compound leaves

In palmately compound leaves, the petiole tip serves as the common place where the leaflets are joined. The leaflets could be sessile or petiolate. Example: silk cotton leaves.

Fig: Palmately compound leaves

Palmately compound leaves are further differentiated into various types:

• Unifoliate
• Bifoliate
• Trifoliate
• Quadrifoliate
• Multifoliate

Unifoliate	Unifoliate leaves have one leaflet as in Citrus. Fig: Unifoliate leaves
Bifoliate	Bifoliate leaves have two leaflets. Examples include Balanites. Fig: Bifoliate leaves
Trifoliate	These types of leaves have three leaflets and all are emerging from the same point. Examples include Oxalis. Fig: Trifoliate leaf
Quadrifoliate	These types of leaves have four leaflets that are arising from the same point. Examples include Marsilea. Fig: Quadrifoliate leaf
Multifoliate	This kind of leaf has numerous leaflets that emerge from a single point as in Bombax. Fig: Multifoliate leaf

Pinnately compound leaves

The midrib creates the rachis, or common axis, along which the leaflets develop, in pinnately compound leaves. Examples include Neem leaves.

Fig: Pinnately compound leaves

Pinnately compound leaves are further differentiated into various types that are listed below:

• Unipinnate, which can either be paripinnate or imparipinnate
• Bipinnate
• Tripinnate
• Decompound

Unipinnate	These types of leaves have leaflets on each side of the axis and the leaflets are directly borne on the rachis. Examples include Cassia. Fig: Unipinnate leaf
Paripinnate	This type of leaf does not have a terminal leaflet. Examples include Cassia.
Imparipinnate	This type of leaf has an odd terminal leaflet. Examples include Pea.
Bipinnate	The central axis creates a secondary axis that bears the leaflets as in Acacia. Fig: Bipinnate leaf
Tripinnate	The secondary axis gives way to a tertiary axis with leaflets as in Moringa. Fig: Tripinnate leaf
Decompound	This type of leaf has more than thrice pinnate. Examples include old leaves of coriander. Fig: Decompound leaf

Practice Problems

Q1. Identify the structure which is not a part of a leaf.

A. Lamina
B. Petiole
C. Stipules
D. Node

Solution: Leaf base refers to the area of the leaf where it connects to the stem. Stipules are a pair of tiny, leaf-like structures that some plants have at the base of their leaves. Stipules are regarded as a portion of the leaf anatomically speaking in a normal flowering plant. Petiole refers to the leaf's stalk. The leaf blade, also known as the enlarged green portion of the leaf, has veins and veinlets. Photosynthesis is mostly carried out by leaf lamina.

The stem has nodes and internodes. Nodes are not part of a leaf. The stem's nodes are where leaves grow. Hence, the correct option is d.

Q2. Determine the incorrect statement about simple leaves.

A. The lamina is undivided
B. The midrib is not touched when the lamina is divided because of the lamina's incisions.
C. The lamina does not bear leaflets
D. Bud is absent in the axil of the petiole of a simple leaf

Solution: When the lamina is intact or when the incisions during division do not touch the midrib, a leaf is said to be simple. The term "compound leaf" refers to a leaf that separates into leaflets at the lamina. The axil of the petiole of the simple leaf and compound leaf contains an axillary bud or lateral bud, while the axil of the leaflet does not. Hence, the correct option is d.

Q3. Identify the plant in which a pinnately compound leaf is present.

A. Hibiscus
B. Mango
C. Neem
D. Silk cotton

Solution: In neem, the leaflets of pinnately compound leaves are arranged on a common axis called the rachis, which arises from the midrib. Hence, the correct option is c.

Q4. Identify the plant in which the complete leaf is modified into the spine.

A. Citrus
B. Aloe
C. Cactus
D. Gloriosa 

Solution: In cacti, an entire leaf is transformed into a spine. It is a xerophyte, therefore the leaves have been transformed into spines to slow down the rate of transpiration. Hence, the correct option is c.

FAQs

Q1. What determines the size of a leaf?
Answer: The size of the leaf is determined by water availability but is limited by the amount of sunlight it receives. Very big leaves would trap more sunlight and easily overheat the plant thus leaves cannot have unlimited growth with increasing water availability. The leaf size grows as long as it wouldn’t overheat the plant.

Q2. Why do leaves possess different colours?
Answer: Leaves possess different types of pigments including the green chlorophyll, red and orange carotenoids and yellow xanthophylls in their chloroplasts. Usually green leaves have high quantities of chlorophyll which masks the other pigments but when chlorophyll is degraded, the other colours peek through. This generally occurs in the fall season when the plants shed their leaves and the supply of nutrients to the dying leaves are cut off. This causes gradual degradation of chlorophyll and the byproducts are mobilised to other viable parts of the plant.

Q3. What is heterophylly?
Answer: Heterophylly is a phenomenon seen in plants due to which different forms of leaves appear on the same plant either due to different phases of development or in response to different environmental conditions. The leaves of coriander show different forms of leaves in the juvenile and mature phases.

Fig: Developmental heterophylly in coriander

Q4. Can plants live without leaves?
Answer: Most plants will die without leaves because they are unable to produce enough nourishment to maintain their structure. However, certain plants have evolved to modify their stems into leaves, which now serve this purpose.

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