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13.2: Monocot Leaves - Biology

13.2: Monocot Leaves - Biology


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Macroscopic Features

Monocot leaves tend to have parallel venation, as opposed to the branching patterns seen in eudicots.

Figure (PageIndex{1}): These two monocot leaves both have parallel venation. It is more obvious in the leaf on the right. However, if you look closely at the leaf on the left, you'll see that those veins do not cross each other. Instead, they travel in the same direction without overlapping, just as in the leaf on the right. Photos by Maria Morrow, CC BY-NC.

Microscopic Features

The model organism for monocots in botany is usually corn (Zea mays). Below, you'll see examples of corn leaf cross sections to demonstrate monocot leaf anatomy. Note that there are approximately the same number of stomata on either side of the leaf, that the vascular bundles are all facing you in cross section (because they run parallel to each other), and that the mesophyll is not divided into two distinct types. Note: There are exceptions. Many monocots will have a more specialized mesophyll arrangement.

Figure (PageIndex{2}): A cross section of a corn (Zea mays) leaf. See the caption in Fig. 13.2.3 for a detailed description of the features present. Photo by Maria Morrow, CC BY-NC.

Figure (PageIndex{3}): A cross section of a section of a corn leaf, labeled. The upper epidermis is composed of parenchyma cells that appear empty. There are two clusters of enlarged cells within the upper epidermis. These are bulliform cells and are not present in the lower epidermis. Stomata occur in approximately even numbers in both the upper and lower epidermis. Eight vascular bundles can be seen, the one on the far right is much larger than the others. In the larger vascular bundle, it is easier to distinguish the large, open vessel elements (stained red). Within the vascular bundle, the xylem tissue is closer to the upper epidermis and the phloem tissue is closer to the lower. Each vascular bundle is surrounded by larger cells with darkly-stained contents. These make up the bundle sheath. The tissue around the vascular bundles is the mesophyll. Photo by Maria Morrow, CC BY-NC.

Bulliform Cells

The bulliform cells present in the upper epidermis are not common to all monocots. This is an adaptation you can find in many grasses that are adapted to hot or dry environments. To avoid water loss, the bulliform cells can contract, causing the leaf to roll up and reduce surface area.

In the image below, you can see a leaf from the beach grass Ammophila rolled in on itself. Can you find the bulliform cells?

Figure (PageIndex{4}): This European beach grass (Ammophila arenaria) leaf has rolled up due to shrinking of the bulliform cells. The upper epidermis is now highly invaginated and located on the inside of the rolled leaf. Image from the Public Domain, sourced from Berkshire Community College Bioscience Image Library.

Figure (PageIndex{5}): This is a close up of the same European beach grass (Ammophila arenaria) leaf as above. The lower epidermis has a thick hypodermis (stained red). A thick cuticle can be seen coating the epidermis. On the right side of the image, there is a fold in the upper epidermis (which has many trichomes). At the folding point, several slightly larger cells can be seen. This is a region of bulliform cells, which allowed the leaf to fold and roll inward. Image from the Public Domain, sourced Berkshire Community College Bioscience Image Library.

Vascular Bundles

In the vascular bundle, the xylem will be on the top (adaxial side) and the phloem will be on the bottom (abaxial side). If you think about the way a leaf emerges from the plant, this matches the way the xylem and phloem are oriented in the stem, with the xylem toward the center of the stem and the phloem closer to the outside/epidermis.

The vascular bundle is often surrounded by inflated parenchyma cells that form a structure called a bundle sheath. In C4 plants, like corn, this is where the Calvin Cycle would take place.

Figure (PageIndex{6}): A vascular bundle of a corn (Zea mays) leaf. There are two vascular bundles in this image. The one on the left is difficult to distinguish and most of what you see are the enlarged bundle sheath cells. The larger vascular bundle on the right has less prominent bundle sheath cells, though they still form a distinct border between the vascular tissue and the mesophyll. The xylem tissue is located closer to the upper epidermis. You can locate it by searching for the large, open cells (vessel elements) with red-stained secondary walls. Below the xylem is the phloem tissue, which encompasses a smaller area. The larger cells in the phloem are sieve tube elements and the smaller ones are companion cells. Image from the Public Domain, sourced from Berkshire Community College Bioscience Image Library.

Below is an image of a vascular bundle in another monocot, Yucca. This vascular bundle has large groups of sclerenchyma cells within it, a smaller group above the xylem and a much larger group below the phloem. How might you distinguish the sclerenchyma cells from the parenchyma cells? Consider the thickness of the cell wall(s) and how each cell type reacts to stains.

Figure (PageIndex{7}): A vascular bundle from a Yucca plant (a monocot). The large groups of thick-walled, red-stained cells are sclerenchyma. These provide rigid support in the region of the vascular bundle. Image from the Public Domain, sourced from Berkshire Community College Bioscience Image Library.

Attributions

Content by Maria Morrow, CC BY-NC


Monocot Root, Leaf, Flower and Plants

The term monocot is short for monocotyledon. The cotyledon is an embryonic leaf in a seed that is the first to emerge when it germinates. Monocot seeds have one cotyledon while dicotyledons, or dicots, have two. Monocots and dicots are two types of angiosperm plants which reproduce using seeds and fruits.

There are about 60,000 species of monocot plants. The largest family are the orchids which have over 20,000 species followed by grasses with 10,000 species. Scientists believe monocots evolved as early as 140 million years ago. Based on pollen grains in the fossil record, the earliest monocots lived in the early Cretaceous period about 120-110 million years ago.

Monocots are found in a variety of habitats. They grow primarily on land but also in rivers, lakes, and ponds, mostly rooted to the bottom but sometimes free-floating. Some also live in intertidal zones near the seashore and a few are marine plants rooted in shallow areas in the ocean.


Features used to Distinguish Monocots from Dicots

Monocots differ from dicots in six distinct structural features. Five of these features are easily observed in the mature angiosperm: the flowers, leaves, roots, stems, and pollen grains. But the root of these differences stem from the very early embryonic stages of the angiosperm, providing the biggest difference of all between monocots and dicots, is the seed.

Flowers

Flowers usually arrange their parts in circles, with the reproductive parts in the middle surrounded by petals and sepals. In monocots, these flower parts are trimerous. In other words, the flower parts of a monocot are arranged, structured, or numbered in multiples of three—usually with one stigma, three stamens, three petals, and a calyx formed by the sepals in numbers less than or equal to the number of petals.

Leaf Veination

Roots

While monocots start of with a tap root, these tap roots tend to die soon after germination and are replaced by adventitious roots. Adventitious roots look fibrous and are spread widely throughout the soil in many different directions. They tend to occupy the upper layer of soil and can be modified for different purposes like additional anchorage or aerial support. Because adventitious roots typically arise from an organ that is not the root of a plant, such as the stem or sometimes a leaf, we are able to grow multiple plants from stem or leaf cuttings of a pre-existing plant!

Stems

It is important to note that the stems of monocots have lost the ability to increase their diameter by producing wood and bark through secondary growth. Instead, monocot stems die down each year, allowing new stems to grow. The only growing point of a monocot stem is at the top of the stem, disallowing the growth of any side stems or branches. Typically, then, monocotyledons are small and herbaceous

In a cross section of a monocot stem, you will find an epidermis, hypodermis, ground tissues, and vascular bundles. Typically, monocot stems have the following characteristics: single layer epidermis with a thick cuticle lack of epidermal hairs lack of concentric arrangement hypodermis is sclerenchymatous presence of bundle sheaths oval vascular bundles of different sizes and most notably, scattered vascular bundles that do not have create any pattern.

Pollen Grains

Monocots have a pollen structure that is retained from the first angiosperms. The pollen grain of a monocot is monosulcate, meaning that the pollen has a single furrow or pore through the outer layer.

Embryos

The plant embryo is the part of the seed that contains all of the precursor tissues of the plant and one or more cotyledon. As the name suggests, monocots are characterized by having one (mono-) cotyledon in the seed, and one leaf emerging from the cotyledon. The seed pod of a monocot is also trimerous (in parts of three), because the carpel from which they grew also consisted of three parts.

The cotyledon is the first part of the plant to emerge from the seed, and is the actual basis for distinguishing the two main groups of angiosperms. Cotyledons are important in food absorption and are responsible for absorbing nutrients from the environment until the plant can photosynthesize its own nutrients.


Example of Monocot Fruits

Banana

Pineapple

Dates

Coconut

Describe on Isobilateral Leaf or Monocotyledonous Leaf

The anatomy of an isobilateral leaf or monocotyledonous leaf is similar to that of the dorsiventral leaf in many ways. It is made up of either only spongy or palisade parenchyma cells. It shows the following characteristic differences. In an isobilateral leaf, the stomata are present on both the surfaces of the epidermis and the mesophyll is not differentiated into palisade and spongy parenchyma (Figure). These types of leaves are similar in appearance on both sides and hence, are called an isobilateral type of leaves.

These types of leaves are found in grasses and monocots e.g., maize. In grasses, certain adaxial epidermal cells along the veins modify themselves into large, empty. colorless cells. Most leaves have certain common features like a covering of an epidermal layer on each surface. These are called bulliform cells. When the bullifon cells in the leaves have absorbed water and are turgid, the leaf surface is exposed. When they are flaccid due to water stress, they make the leaves curl inwards to minimize water loss. The parallel venation in monocot leaves is reflected in the near similar sizes of vascular bundles (except in main veins) as seen in vertical sections of the leaves. The ground tissue that occurs between the two epidermal layers is called mesophyll. Vascular bundles, generally known as veins, are embedded in the mesophyll. The organization and characteristics of each of these layers differ significantly for dorsiventral and isobilateral leaves.

Based on the approach of course to the main axis of plant and direction of sunlight, leaves in angiosperms can be divided into two types

Dorsi-ventral leaves– These leaves orient themselves at an angle to the major axis and vertical to the direction of sunlight. Most dicots have dorsiventral leaves that are net-veined, including most trees, bushes, garden plants and wildflowers.

Isobilateral leaves – These leaves orient themselves parallel to the major axis and parallel to the direction of sunlight. Most monocots possess parallel-veined isobilateral leaves, including grasses and grasslike plants, lilies, irises, amaryllises, etc.

Internal Structure of Monocot or Isobilateral Leaf –


Evolution

Monocots form a monophyletic group, meaning that they share a common evolutionary history. It is widely believed that the monocots were derived from primitive eudicots. Given that the various physical features of monocots are regarded as derived characteristics within the angiosperms, any plant more primitive than the monocots in these several respects would certainly be a eudicot. Some of the earliest known monocot fossils are pollen grains dating to the Aptian Age of the Early Cretaceous Epoch (125 million–113 million years ago). Molecular clock studies (which employ differences in DNA to estimate when a group split from its ancestors) suggest that monocots may have originated as early as 140 million years ago.

Evolutionary diversification among the monocotyledons appears to have been constrained by a number of fundamental features of the group, most notably the absence of a typical vascular cambium and the parallel-veined rather than net-veined leaves. Within these constraints, the monocots show a wide range of diversity of structure and habitat. They are cosmopolitan in their distribution on land. They also grow in lakes, ponds, and rivers, sometimes free-floating but more often rooted to the bottom. Some of them grow in the intertidal zone along the seashore, and a few are submerged marine plants rooted to the bottom in fairly shallow water along the shore.


161 Leaves

By the end of this section, you will be able to do the following:

  • Identify the parts of a typical leaf
  • Describe the internal structure and function of a leaf
  • Compare and contrast simple leaves and compound leaves
  • List and describe examples of modified leaves

Leaves are the main sites for photosynthesis: the process by which plants synthesize food. Most leaves are usually green, due to the presence of chlorophyll in the leaf cells. However, some leaves may have different colors, caused by other plant pigments that mask the green chlorophyll.

The thickness, shape, and size of leaves are adapted to the environment. Each variation helps a plant species maximize its chances of survival in a particular habitat. Usually, the leaves of plants growing in tropical rainforests have larger surface areas than those of plants growing in deserts or very cold conditions, which are likely to have a smaller surface area to minimize water loss.

Structure of a Typical Leaf

Each leaf typically has a leaf blade called the lamina , which is also the widest part of the leaf. Some leaves are attached to the plant stem by a petiole . Leaves that do not have a petiole and are directly attached to the plant stem are called sessile leaves. Small green appendages usually found at the base of the petiole are known as stipules . Most leaves have a midrib, which travels the length of the leaf and branches to each side to produce veins of vascular tissue. The edge of the leaf is called the margin. (Figure) shows the structure of a typical eudicot leaf.


Within each leaf, the vascular tissue forms veins. The arrangement of veins in a leaf is called the venation pattern. Monocots and dicots differ in their patterns of venation ((Figure)). Monocots have parallel venation the veins run in straight lines across the length of the leaf without converging at a point. In dicots, however, the veins of the leaf have a net-like appearance, forming a pattern known as reticulate venation. One extant plant, the Ginkgo biloba, has dichotomous venation where the veins fork.


Leaf Arrangement

The arrangement of leaves on a stem is known as phyllotaxy . The number and placement of a plant’s leaves will vary depending on the species, with each species exhibiting a characteristic leaf arrangement. Leaves are classified as either alternate, spiral, or opposite. Plants that have only one leaf per node have leaves that are said to be either alternate—meaning the leaves alternate on each side of the stem in a flat plane—or spiral, meaning the leaves are arrayed in a spiral along the stem. In an opposite leaf arrangement, two leaves arise at the same point, with the leaves connecting opposite each other along the branch. If there are three or more leaves connected at a node, the leaf arrangement is classified as whorled .

Leaf Form

Leaves may be simple or compound ((Figure)). In a simple leaf , the blade is either completely undivided—as in the banana leaf—or it has lobes, but the separation does not reach the midrib, as in the maple leaf. In a compound leaf , the leaf blade is completely divided, forming leaflets, as in the locust tree. Each leaflet may have its own stalk, but is attached to the rachis. A palmately compound leaf resembles the palm of a hand, with leaflets radiating outwards from one point. Examples include the leaves of poison ivy, the buckeye tree, or the familiar houseplant Schefflera sp. (common name “umbrella plant”). Pinnately compound leaves take their name from their feather-like appearance the leaflets are arranged along the midrib, as in rose leaves (Rosa sp.), or the leaves of hickory, pecan, ash, or walnut trees.


Leaf Structure and Function

The outermost layer of the leaf is the epidermis it is present on both sides of the leaf and is called the upper and lower epidermis, respectively. Botanists call the upper side the adaxial surface (or adaxis) and the lower side the abaxial surface (or abaxis). The epidermis helps in the regulation of gas exchange. It contains stomata ((Figure)): openings through which the exchange of gases takes place. Two guard cells surround each stoma, regulating its opening and closing.


The epidermis is usually one cell layer thick however, in plants that grow in very hot or very cold conditions, the epidermis may be several layers thick to protect against excessive water loss from transpiration. A waxy layer known as the cuticle covers the leaves of all plant species. The cuticle reduces the rate of water loss from the leaf surface. Other leaves may have small hairs (trichomes) on the leaf surface. Trichomes help to deter herbivory by restricting insect movements, or by storing toxic or bad-tasting compounds they can also reduce the rate of transpiration by blocking air flow across the leaf surface ((Figure)).


Below the epidermis of dicot leaves are layers of cells known as the mesophyll, or “middle leaf.” The mesophyll of most leaves typically contains two arrangements of parenchyma cells: the palisade parenchyma and spongy parenchyma ((Figure)). The palisade parenchyma (also called the palisade mesophyll) has column-shaped, tightly packed cells, and may be present in one, two, or three layers. Below the palisade parenchyma are loosely arranged cells of an irregular shape. These are the cells of the spongy parenchyma (or spongy mesophyll). The air space found between the spongy parenchyma cells allows gaseous exchange between the leaf and the outside atmosphere through the stomata. In aquatic plants, the intercellular spaces in the spongy parenchyma help the leaf float. Both layers of the mesophyll contain many chloroplasts. Guard cells are the only epidermal cells to contain chloroplasts.


Like the stem, the leaf contains vascular bundles composed of xylem and phloem ((Figure)). The xylem consists of tracheids and vessels, which transport water and minerals to the leaves. The phloem transports the photosynthetic products from the leaf to the other parts of the plant. A single vascular bundle, no matter how large or small, always contains both xylem and phloem tissues.


Leaf Adaptations

Coniferous plant species that thrive in cold environments, like spruce, fir, and pine, have leaves that are reduced in size and needle-like in appearance. These needle-like leaves have sunken stomata and a smaller surface area: two attributes that aid in reducing water loss. In hot climates, plants such as cacti have leaves that are reduced to spines, which in combination with their succulent stems, help to conserve water. Many aquatic plants have leaves with wide lamina that can float on the surface of the water, and a thick waxy cuticle on the leaf surface that repels water.

Watch “The Pale Pitcher Plant” episode of the video series Plants Are Cool, Too, a Botanical Society of America video about a carnivorous plant species found in Louisiana.

Plant Adaptations in Resource-Deficient Environments Roots, stems, and leaves are structured to ensure that a plant can obtain the required sunlight, water, soil nutrients, and oxygen resources. Some remarkable adaptations have evolved to enable plant species to thrive in less than ideal habitats, where one or more of these resources is in short supply.

In tropical rainforests, light is often scarce, since many trees and plants grow close together and block much of the sunlight from reaching the forest floor. Many tropical plant species have exceptionally broad leaves to maximize the capture of sunlight. Other species are epiphytes: plants that grow on other plants that serve as a physical support. Such plants are able to grow high up in the canopy atop the branches of other trees, where sunlight is more plentiful. Epiphytes live on rain and minerals collected in the branches and leaves of the supporting plant. Bromeliads (members of the pineapple family), ferns, and orchids are examples of tropical epiphytes ((Figure)). Many epiphytes have specialized tissues that enable them to efficiently capture and store water.


Some plants have special adaptations that help them to survive in nutrient-poor environments. Carnivorous plants, such as the Venus flytrap and the pitcher plant ((Figure)), grow in bogs where the soil is low in nitrogen. In these plants, leaves are modified to capture insects. The insect-capturing leaves may have evolved to provide these plants with a supplementary source of much-needed nitrogen.


Many swamp plants have adaptations that enable them to thrive in wet areas, where their roots grow submerged underwater. In these aquatic areas, the soil is unstable and little oxygen is available to reach the roots. Trees such as mangroves (Rhizophora sp.) growing in coastal waters produce aboveground roots that help support the tree ((Figure)). Some species of mangroves, as well as cypress trees, have pneumatophores: upward-growing roots containing pores and pockets of tissue specialized for gas exchange. Wild rice is an aquatic plant with large air spaces in the root cortex. The air-filled tissue—called aerenchyma—provides a path for oxygen to diffuse down to the root tips, which are embedded in oxygen-poor bottom sediments.


Watch Venus Flytraps: Jaws of Death, an extraordinary BBC close-up of the Venus flytrap in action.

Section Summary

Leaves are the main site of photosynthesis. A typical leaf consists of a lamina (the broad part of the leaf, also called the blade) and a petiole (the stalk that attaches the leaf to a stem). The arrangement of leaves on a stem, known as phyllotaxy, enables maximum exposure to sunlight. Each plant species has a characteristic leaf arrangement and form. The pattern of leaf arrangement may be alternate, opposite, or spiral, while leaf form may be simple or compound. Leaf tissue consists of the epidermis, which forms the outermost cell layer, and mesophyll and vascular tissue, which make up the inner portion of the leaf. In some plant species, leaf form is modified to form structures such as tendrils, spines, bud scales, and needles.

Review Questions

The stalk of a leaf is known as the ________.

Leaflets are a characteristic of ________ leaves.

Cells of the ________ contain chloroplasts.

Which of the following is most likely to be found in a desert environment?

  1. broad leaves to capture sunlight
  2. spines instead of leaves
  3. needle-like leaves
  4. wide, flat leaves that can float

Critical Thinking Questions

How do dicots differ from monocots in terms of leaf structure?

Monocots have leaves with parallel venation, and dicots have leaves with reticulate, net-like venation.

Describe an example of a plant with leaves that are adapted to cold temperatures.

Conifers such as spruce, fir, and pine have needle-shaped leaves with sunken stomata, helping to reduce water loss.

Glossary


Comparison between Monocot and Dicot Plants

There are some specific characteristics that help us identify the plant as a monocot or a dicot. Let us look at them.

Seeds

Plant embryos in seeds have structures called cotyledons. A cotyledon is the central portion of a seed embryo to which the epicotyl (immature shoot) and radicle (immature root) are attached. The number of cotyledons differs in these two groups of plants and that forms the basis for the main classification of monocots and dicots. A seed of a monocot plant has one cotyledon and that of a dicot plants has two cotyledons. (Note: This is easy to remember when you know mono=one and di=two).

Roots

Roots can develop either from a main radicle that is one large taproot with many small secondary lateral roots growing out of it, or can be a fibrous mass of roots that arise from the nodes in the stem, called adventitious roots. Monocots have adventitious roots, whereas dicots have a radicle from which a root develops.

Leaves

Leaves have more than one characteristic that help differentiate a monocot from a dicot. If the leaf has a stalk, then the plant is a dicot. But, in the case of a monocot plant, the leaf is sessile, which means it is attached directly by its base without a stalk.

The next characteristic that helps in the identification is the venation. If the leaves have parallel venations that are long and thin, then the plant is monocot. If the leaves have a branched venation, then the plant is a dicot.

Flowering Parts

Monocot flowers tend to have a number of petals or other floral parts that is divisible by three, usually three or six. Dicot flowers on the other hand, are likely to have parts in multiples of four or five (four, five, ten, etc.). This character is not always reliable, and is not easy to use in identification of some flowers with reduced or numerous parts.

Pollen Structure

Monocot and dicot plants have different pollen structures. In a monocot, the pollen grain produced by the flower has a single furrow or pore through the outer layer. In a dicot plant, the pollen grain has three furrows or pores.

Stem & Vascular Bundles

Monocot plants normally have a weak stem, whereas dicots have a strong stem. Vascular tissues are seen as long strands and are called vascular bundles. In the dicot plant, the vascular bundles are arranged in a ring form, whereas in a monocot, these bundles appear scattered through the stem, with more of the bundles located towards the periphery (outer edge) of the stem than at the centre.

Note: There are some exceptions to this classification however, as some species of plants belonging to monocots can have characters belonging to dicots, since the two groups have a shared ancestry.


Distinguishing Characteristics Between Monocots & Dicots: Leaf Veins

Angiosperms, or flowering plants, can be classified as either a monocot or a dicot. The terms monocot and dicot actually refer to the cotyledons, or embryonic leaves that first appear on the plant embryo. A monocot has only one cotyledon and a dicot has two. However, the number of cotyledon is only one of five distinguishing characteristics. Another identifying trait is the leaf veins. Monocots generally have parallel leaf veins whereas the leaf veins of dicots are generally multibranched.

This picture is of Fakahatchee grass (Tripsacum dactyloides). The leaf clearly displays the parallel leaf veins of a monocot.

This picture shows the leaf of a wild coffee plant (Psychotria nervosa). The veins of this leaf branch out, revealing the plant to be a dicot.


Content: Dicot Vs Monocot Leaf

Comparison Chart

PropertiesDicot leafMonocot leaf
SymmetryDorsiventralIsobilateral
ShapeBroad or palmateLong and slender
Colour of upper leaf surfaceDark greenBoth the upper and lower surfaces are equally green
Colour of lower leaf surfaceLight green
VeinsNet or reticulate veins
Parallel veins
StomataFound in lower surfaceEqually distributed in both the surfaces
Arrangement of stomataPresent randomlyArranged in parallel rows
Guard cellsKidney shaped
Dumb-bell shaped
MesophyllDifferentiatedUndifferentiated
Bundle sheathSingle layeredOne or more than one layer
Colour of bundle sheathColourlessColoured due to abundance of chloroplast
Extensions of bundle sheathParenchymatousIt is both Parenchymatous and Schlerenchymatous
Lateral wallSinuous/CurvyStraight
Bulliform/Motor cellsAbsentPresent
Vascular bundlesLargeSmall and large both
Arrangement of vascular bundlesPresent in rowsPresent randomly
Intercellular spaceLargeSmall
Silica deposition on epidermal cellsAbsentPresent
Hypodermis of mid ribCollenchymatousSchlerenchymatous
TrichomeAbsentPresent
ExamplesLeguminous plants (pea, beans, peanuts etc.), tomato, brinjal, oak leaf etc.Leaf of grains (Wheat, corn, rice etc.), banana, bamboo etc.

Definition of Dicot Leaf

The dicot leaves are non-linear, unlike monocot leaves and the vascular bundles in them are irregularly arranged in the net-like veins. These are hypostomatous, i.e. possess stomata on one side (lower epidermis) and have reticulate venation pattern. Dicot leaves comprise the mesophyll differentiated into compactly-arranged palisade and loosely arranged spongy parenchyma cells.

Definition of Monocot Leaf

The monocot leaves are generally linear or oblong and the vascular bundles in them are parallel arranged in the striated veins. These are amphistomatous, i.e. possess stomata on both the sides (upper and lower epidermis) and have striate venation. Here, the mesophyll is undifferentiated.

Diagram

The main characteristic feature to distinguish the dicot and monocot leaf is the type of venation a leaf have. One can easily observe either the veins are striking or parallel by seeing a leaf. Below is the diagram of dicot and monocot leaf, where we can see the venation pattern.

Anatomy of Dicot Vs Monocot Leaf

To know the whole concept of dicot and monocot leaf cell, there are some properties which are as follows:

Symmetry

Dicot leaf shows dorsiventral symmetry where both the dorsal and ventral surface are distinguishable, whereas monocot leaf shows isobilateral symmetry where both the dorsal and ventral surface is similar.

Cuticle

It is the outer waxy envelope that covers the epidermis layer. Dicot leaf has a thin layer of cuticle on both the upper and lower epidermis, whereas monocot leaf has thick cuticle on the upper epidermis and thin on lower epidermis.

Epidermis

It is a secondary covering that protects the internal cells against damage. It divides into:

Monocot leaf has the same epidermis layer due to equal distribution of stomata. In contrast, the stomata in dicot leaf are present mostly in the lower epidermis and less or no stomata on the upper epidermis.

Mesophyll

These are the cells that are present below the epidermis. It is the middle layer of a leaf that constitute the most of the leaf. It has a high number of chloroplasts that shows photosynthetic activity. In dicot leaf the mesophyll is differentiated into two cells:

  1. Upper palisade mesophyll: These are elongated cylindrical cells and arranged in the parallel fashion inner to the upper epidermis. Palisade mesophyll contains less or no intercellular space because these lack air cavities.
  2. Lower spongy mesophyll: These are rounded cells, which are arranged loosely. Spongy mesophyll present near the lower epidermis. It has large intercellular space because of the presence of air cavities.

Oppositely, undifferentiated mesophyll is present in the monocot leaves. It has only spongy mesophyll, which is spherical in shape and is compactly arranged.

Vascular bundle

It consists of vascular tissues xylem and phloem that plays a significant role in the transportation process. Xylem helps in water transportation which contains vessels, tracheids etc. Phloem contains sieve tubes and companion cells that help in food transportation. The size of the vascular bundle depends upon the size of veins.

In dicot leaf, the vascular bundle is present centrally. The vascular bundle is conjoint, collateral and closed, which is encircled by a single-layered bundle sheath. In monocot leaf, the vascular bundle present parallel in each row. It has collateral and closed vascular bundle that is encased by both parenchymatous and sclerenchymatous bundle sheath.

Stomata and sub stomal cavities

In dicot leaf, stomata and sub stomal cavities are present on the lower epidermis. whereas a monocot leaf possesses stomata and sub stomal cavities on both the upper and lower epidermis.

Bulliform cells

These are the large, colourless, empty cells that attach to the upper epidermis and play a significant function in rolling and unrolling of leaves. In dicot leaf, bulliform cells are absent, whereas present in a monocot leaf.


Monocots and Dicots: Characteristics and Differences

Plants can be broadly divided into two types: flowering plants and non-flowering plants. In this case, flowering plant is also known as angiosperms while non-flowering plant is known as gymnosperms. Based on the nature of the embryo in the seed, angiosperms are again divided into the following two types:

Monocotyledonous Plants

Monocotyledon is commonly known as monocot. They have seeds with one embryonic leaf or cotyledon hence they are called monocotyledonous plants. This group contains about 60,000 species. Among them, the family Orchidaceae (orchids) contains more than 20,000 species. Besides these, the Poaceae (true grasses) is the most important family. Other prominent monocot families include Arecaceae (palms), bananas, plantains (Musaceae), Liliaceae (lilies), and Iridaceae (irises). This group includes different type of grains (rice, wheat, maize, etc.), forage grasses, sugarcane, the bamboos, etc.