Monocot Vs Dicot Leaves Overview

Definition of Monocot Leaves

It is common to utilise the thin, elongated, parallel venation of monocotyledonous leaves to identify monocotyledonous plants from dicots.

• Since the colour on both sides of monocot leaves is the same, they are isobilateral.
• The proximal leaf bottom, or hypophyll, as well as the distal leaf surface, or hyperphyll, comprise the primordial monocot leaves. In dicots, the hyperphyll predominates in the leaf, whereas in monocots, the hypophyll is the predominant component.
• There are several outliers among monocots that may not have identical features. However, the leaves are often thin and linear, with a sheath around the stem at its base.
• As noted earlier, the venation is striate, predominantly longitudinally striate but rarely palmate-striate or pinnate-striate.
• The leaf’s surface veins begin to appear from the base and progress jointly to the tip.
• As the leaf base occupies greater than half of the circumference of the stem, most monocotyledonous plants possess merely one leaf per node.
• The occurrence of a larger leaf base at zonal differentiation has been connected to differential stem development.

Definition of Dicot Leaves

• Dicotyledonous leaves often have rounder shapes and reticulate venation, which set them apart from monocotyledonous leaves in terms of morphology and structure. A lead blade, sometimes called a lamina, makes up the majority of a typical dicot leaf. The largest area of a leaf is called the lamina.
• Dicot leaves are dorsoventral due to the colouring of the leaves, which makes it possible to distinguish between the dorsal and ventral portions of the leaves. Typically, a leaf’s dorsal side has greater pigmentation than its ventral side.
• Unlike monocot leaves that are attached directly to the stem, dicot leaves are usually connected to the stem via a petiole.
• Some dicot leaves may have tiny green protrusions called stipules at the bottom of the petiole. 
• The midrib of dicot leaves stretches the entire length of the leaf and runs through the leaf blade. Multiple branches develop on either side of the midrib, resulting in reticulate venation.
• Dicots typically have 2 or many leaves coming from a single node, although the quantity of leaves per node differs per species.
• Dicot leaves can be subsequently subdivided depending on their leaf structure, with a few species having simple leaves and many others possessing complex leaves.

Structure of Monocot and Dicot Leaves

The internal anatomy or structure of monocot as well as dicot leaves can be determined based on the following structures:

1, Epidermis

• The outermost tissue of leaves is called the epidermis, and it is made up of a layer of tightly packed cells with thin walls that resemble barrels. Both the upper and bottom halves of the leaf include the epidermis.
• The cuticle, an exterior waxy layer that serves to shield the leaf and stop water loss, is located around the epidermis.
• Because dicot leaves are dorso-ventral, the cuticle of the leaf’s top surface is broader than that of the lower surface. However, in monocots, the epidermis layer is roughly the same thickness on both sides.
• The epidermis is essential because, like a waxy, watertight layer, it prevents excess water evaporation. Furthermore, it possesses small holes called stomata. It also significantly contributes to gas exchange.
• For monocot leaves, the quantity of stomata on either side is similar. Dicot leaves have more stomata on the lower epidermis than on the top epidermis. 
• The guard cells, which are bean-shaped cells that control the size of the stomata, are found between the stomata as a little aperture. In dicots, the guard cells are formed like dumbbells.
• Chloroplasts, which give the leaves their distinctive green hue, are present in the guard cells but not in the epidermal cells.
• In addition to the epidermal cells and the guard cells, the epidermis also has extra cells called subsidiary cells that are frequently found near the guard cells.
• Bulliform cells, also known as motor cells, are big, thin-walled cells found in the top epidermis of dicot cells. In response to a change in weather, these cells help the leaves roll.
• Silica cells are epidermal cells that are packed with silica in monocot leaves.

2. Mesophyll

• The ground tissue of leaves, or mesophyll, is located between the top and lower epidermis of the leaves.
• While monocot leaves lack this division, dicot leaves have palisade parenchyma and spongy parenchyma.
• Directly under the top epidermis lies a layer of tissue called the palisade parenchyma. It consists of one or more layers of cylindrical cells that are vertically extended. There are no intercellular gaps between the tightly packed cells.
• Compared to the cells of the spongy parenchyma, the palisade parenchyma cells contain more chloroplasts.
• Below the palisade parenchyma, where the cells are unevenly formed, lies the spongy parenchyma. Compared to palisade parenchymal cells, these cells have fewer chloroplasts.
• The word “spongy parenchyma” refers to the loosely packed cells and various gaps that make up its structure. These air holes facilitate the passage of gases between the cells. The spaces located next to stomata are referred to as respiratory cavities or sub-stomatal cavities.
• The isodiametric, thin-walled cells that make up the mesophyll of dicot leaves are not differentiated into palisade or spongy parenchyma.
• The densely packed cells have a few intercellular air spaces.

3. Vascular Bundles

• The vascular bundle, located beneath the mesophyll and along the leaf veins, is the deepest layer of plant tissue.
• Not all vascular bundles contain similar sized vessels; the larger bundles emerge at frequent intervals throughout the veins. There are two clusters of sclerenchyma cells atop and under the primary arterial bundles.
• The vascular system of the plant, which traverses several organs and encircles the entire organism, includes the vascular bundles of the leaves.
• In respect of size and placement, leaf vascular bundles display a wide variety of arrangements.
• Dicot leaves feature veins of varied diameters that form a highly branched network. Thus, several vascular bundles are found beneath these veins.
• Since the longitudinal veins lie parallel throughout the leaf blade and are linked transversely by short commissural veins, monocot leaves possess fewer diverse vascular bundles.
• A bundle sheath encircles the conjoint, collateral, and closed vascular bundles. Dicot leaves have a sclerenchymatous sheath rather than a parenchymatous bundle sheath.
• The vascular bundle contains xylem tissue toward the upper epidermis and phloem tissue toward the lower epidermis.
• Both vessels and xylem parenchyma make up the xylem. Metaxylem and protoxylem are the two types of xylem found in monocot leaves. Sieve cells, companion cells, and phloem parenchyma make up the phloem.

Functions of Monocot and Dicot Leaves

Both dicot and monocot plants use their leaves for similar purposes in most cases.

1. The functions of leaves vary depending on the kind of plant, the environment, and the age of the leaf. Among the duties performed by monocot and dicot plants are the following:
2. The production of food through the process of photosynthesis is the most significant role played by leaves in green plants. Chlorophyll is present in the leaf cells because one-fifth of the mesophyll cells have chloroplasts that contain chlorophyll. The leaves’ broad, huge surface area enables them to absorb more sunlight, which is necessary for photosynthesis.
3. The cuticle and epidermis of the leaves stop excessive water loss during transpiration, preventing the plant from drying out.
4. Stomata, which are a component of the leaves, are crucial for the transpiration process, which moves water from the plant into the atmosphere. This is required so that the roots can absorb water carrying nourishment from the earth.
5. In addition to facilitating transpiration, stomata also facilitate the exchange of gases. The stomata take carbon dioxide from the environment and discharge oxygen during photosynthesis.
6. The food produced in the cells in the leaves of certain plants, like cabbage and lettuce, is stored in various ways in the leaves.

Examples of Monocot Leaves

1. Maize leaves

• With their straightforward and systematic structures, maize leaves are said to be the most typical monocot leaves.
• There are typically 20 leaves on a maize plant, and they might be at various stages of growth. A mature maize leaf is approximately 70 cm long and 8 cm wide.
• The three parts of a maize leaf are the upper blade, bottom sheath, and auricle. To create parallel lines and an extended appearance, the leaf cells are tightly aligned and directed.
• The mesophyll and vascular tissue are enclosed by adaxial and abaxial epidermal tissue in the maize leaf blade.
• The specialised cells and nonspecialized intercostal cells that make up the maize leaf’s epidermis are two different types of cells.
• Specialized cells consist of stomatal complexes and three distinct kinds of hair cells, including large macrohairs, microbars, and bicellular hairs. These cells have a protective function.

2. Grass

• A grass leaf is a monocot leaf with an elongated structure that emerges from the node and is composed of younger leaves and a basal cylindrical sheath that envelops the stem.
• On the outside are sheaths, which are hollow cylinders that are divided along one side. Typically, these sheaths produce structures that overlap.
• The auricle on the leaf may take the form of an ear-like protrusion or it may just be a hairy edge near the base of the leaf blade.
• The epidermis of a grass leaf is composed of specialised hair cells which guard the plant against several diseases.
• Due to their variability across species or even within the same plant, the form, texture, and hairiness of the leaves are frequently employed as diagnostic traits to distinguish grass from other plants.

Examples of Dicot Leaves

1. Mustard leaves

• As a typical dicot plant, mustard is frequently used in research on dicotyledonous plants.
• When the leaves are 6-8 inches long, mustard leaves start to grow within 4 weeks. In around 6 weeks, a mature mustard leaf reaches a length of 15 to 18 inches.
• The large, green leaves have reticulate venation. The ventral surface of the leaves is lighter than the dorsal surface, and they are dorsoventrally flattened.
• A few specialised hair cells that guard against water loss and toxic substances are present in the epidermis of mustard leaves.
• Since mustard leaves provide nutritional benefits for human health, they are used as vegetables.

2. Mint leaves

• The leaves of the quickly expanding plant known as mint are round and lanceolate, and they are placed on the stalk in opposing pairs.
• The leaves are tiny and have a length of 4-5 inches. However, the maturity and age of the leaves determine the size of the leaves.
• The reticulate venation of the leaves has a central midrib from which branching veins protrude.
• On both the upper and lower surfaces of the leaves, there are little hairs that cover the surface.
• Mint leaves have a distinctive mint smell that makes them pleasant. Different civilizations employ these leaves as species in various foods.

References and Sources

• Lee Yuen Lew (2000) Storage Organs and Plant Growth, Science Activities, 37:2, 39-46, DOI: 10.1080/00368120009603566
• Nelissen H, Gonzalez N, Inzé D. Leaf growth in dicots and monocots: so different yet so alike. Curr Opin Plant Biol. 2016 Oct;33:72-76. doi: 10.1016/j.pbi.2016.06.009. Epub 2016 Jun 23. PMID: 27344391.
• Sylvester A.W., Smith L.G. (2009) Cell Biology of Maize Leaf Development. In: Bennetzen J.L., Hake S.C. (eds) Handbook of Maize: Its Biology. Springer, New York, NY. https://doi.org/10.1007/978-0-387-79418-1_10
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