LEAF: Definition
The Leaf is a lateral appendage that develops at the nodal area of the stem and is flat and green. When the leaves are simply on the main axis, it is termed Cauline, and when the leaves are on the lateral branches, it is called Ramal.
A typical Dicot leaf has three segments.
1. Leaf base
2. Petiole
3. Lamina
1. Leaf base: The “Leaf base” is the point where the Leaf joins to the stem.
2. Petiole: It refers to the short cylindrical stem of the leaf. Petiolate refers to a leaf with a petiole, while ‘Sessile’ refers to a leaf without one.
3. Stipule: A pair of lateral tiny green outgrowths called ‘Stipules’ emerge from the base of the Petiole. Stipulate refers to a leaf with a stipule. Ex stipulate refers to a leaf without a stipule.
4. Lamina: “Lamina” or “Leaf blade” refers to the flat, green, enlarged section of the Lamina. The “Leaf apex” is the point of the lamina, and the “Leaf margin” is the edge of the lamina. It could be smooth, whole, serrate, undulate, dentate, or spiny. Lamina comes in a variety of shapes and sizes.
5. The Mid-rib: The “Mid rib,” which runs from the Petiole to the apex in the center of the Lamina, is the primary Vasculature. It creates a variety of “Veins” that are distributed in various ways. These are secondary arteries and veins (Transport water, dissolved salts, and organic food). It produces beautifully branching “Veinlets.”
A)Leaf form: Leaf properties such as shape, texture, and arrangement are taxonomic and are employed in flowering plant categorization.
B) Leaf Margin: The ‘Leaf margin’ refers to the margin of a Lamina. It can be found in a variety of forms
1. Entire: The entire edge of the margin is smooth. Example Mango
2. Undulate or wavy: The edge is wavy. A nice example is Polyathia.
3. Serrate-margin: It is a type of tooth that looks like a saw blade. Example Rose, and Hibiscus.
4. The dentate-margin has teeth. Water Lilly, for example.
5. Spiny- The margin has a spiny texture. Datura is a good example.
B) Leaf Form:
1. Linear: a straight line that is uniformly long, narrow, and flat.
For instance, grass.
2. Lanceolate: The apical section of the plant is tapered and lance-shaped. Consider the case of Nerium.
3. Oblong: The base and apex are both uniformly long and rounded.Example Banana
4. Elliptical: Longer than broad, with a constant width.Example Guava,
5. Ovate: Egg-shaped, with a broad base and a narrowing apex.
6. Cordate: It means “heart-shaped.” Consider the case of Betel.
C) Leaf surface:-
a. Glabrous: The surface of the leaf is smooth.Example Mango
b. Hairy: Hair covers the entire surface.Example Tomato
c. Glaucus: Waxy coating on the surface.Example Calotropis
D) Texture of the Leaf:
A. Due to the accumulation of water in the form of mucilage, the lamina is thick and soft. Example Aloe vera, for example.
B. The lamina of coriaceous plants is hard, dry, and leathery. Example Sapota
VENATION
Veins are rib-like, linear structures in the leaf blade that emerge from the mid-rib. It causes lateral Vein lets to form. Venation refers to the distribution and arrangement of veins and veinlets within the leaf’s lamina. It represents the fibrovascular tissue system’s ramifications. The veins and veinlets are arranged in a certain way. In the case of Lamina,
Venation is divided into two categories
There are two types of venation:
1) Reticulate venation
2) Parallel venation.
1. Reticulate Venation: Veins and Veinlets are frequently branched to form a network or Reticulum in Reticulate Venation. A good example is a dicot leaf. It is then subdivided into the following groups:
A. Unicostate (Pinnate type): In this kind, a single midrib produces lateral veins on both sides, similar to feather plumes. Peepal is a good example.
B. Multicostate (type Palmate): Two or more veins emerge from the base of the Lamina in this kind. It could be either divergent or convergent.
a) Multicostate Convergent type: Two or more main veins emerging from the leaf base converge towards the leaf apex in this type. Example Ziziphus,
b) Multicostate Divergent: Two or more main veins emerge from the leaf base and diverge toward the leaf margin in this form. Example Castor.
2) Parallel Venation:-
All major veins run parallel to one another from the midrib to the margin, or from the base to the apex of the leaf, in Parallel Venation. Consider the leaf of a monocot. The following are the subcategories:
A.Parallel Unicostate: A single midrib and veins run parallel to each other in this form. Canna is a good example.
B. Parallel multicostate: This type of multicostate has two or more primary veins that emerge from the base, pass through the lamina, and converge at the apex, as in bamboo. Or, as in the palm, diverge towards the margin, known as ‘Multicostate Divergent.’
THE DIFFERENT TYPES OF STIPULES
A stipule is a tiny leafy appendage located near the base of the leaf. It shields the leaf when it is in the bud stage. Stipulate refers to a leaf with a stipule. A leaf with no stipule is known as “ex stipulates.”
TYPES OF STIPULES
1. Free Lateral: Little greenish outgrowths on either side of the leaf base are known as “free laterals. It is the most basic sort of stipulation. Hibiscus and Gossypium are two examples.
2. Adnate(Adherent): Two lateral stipules joined over a distance with the petiole, generating a wing-like shape.Example Rose
3. Interpetiolar: Stipules are present between the petioles of opposing leaves in this kind. Hamelia is a good example. Coffee.
4. Foliaceous: Stipules in this variety are big, green, and have a leaf-like shape.Example Pea
5. Ochreate: Stipules fuse from a tubular structure enveloping the stem above the node up to a particular height in this type.
PHYLLOTAXY
“Phyllotaxy” refers to the pattern of leaf arrangement on the stem’s nodes and branches. It comes from the Greek word phyllon, which means leaf, and taxis, which means arrangement. The following are the several types of phyllotaxy:-
1. Alternate (Spiral): Alternate is a type of type. Each node has a single leaf that alternates. Alternatively, in a spiral around the stem. Example Hibiscus
2. Opposite: In the Opposite kind, two leaves are opposite one other at each node.
A) In Opposite Decussate, each node produces a pair of leaves with alternating planes at right angles to each other. Calotropis and Ixora are two examples.
B)In Opposite Superposed, A pair of leaves appear in the same plane at successive nodes. Example Guava
3. Whorled: Phyllotaxy in which three or more leaves appear in whorls at each node is known as Whorls Phyllotaxy. Consider the case of Nerium.
THE MANY TYPES OF LEAF
Using the number of leaf blades per petiole as a guide There are two sorts of leaves. Simple and compound leaves are the two types of leaves.
1. Leaf, Simple:
“Simple leaf” refers to a leaf with only one lamina.
2. Compound leaves:
A compound leaf is a leaf with several leaflets placed on Rachis. (Lamina is divided into numerous small independent components known as ‘Leaflets.’) The rachis is the compound leaf’s petiole.
Compound Leaf Types
Compound leaves are categorized into two categories based on the arrangement of leaflets:
I.Pinnately compound leaf
II.Palmately compound leaf
I. Leaf with a pinnately compound structure:
Leaflets appear along the sides of the rachis in Pinnately compound leaves. It comes in the following varieties:-
Unipinnate: Leaflets emerge on the Primary rachis in this form.
a)Rachis that ends in a pair of Leaflets is known as a “Paripinnate leaf.Example Tamarind
b)Rachis that ends in a single Leaflet is referred to as an “Immaparipinnate leaf. Example Rose
2. Bipinnate: Leaflets develop on secondary rachis in this type.Example Mimosa pudica
3. Tripinnate: Leaflets develop on the tertiary rachis in this type. Example Moringa
4. Decompound: Rachis is a multi-branched plant with leaflets on the ultimate branches.Example Coriander
II Palmately compound leaf
Leaflets emerge from a single point at the tip of the petiole in palmately compound leaves. It belongs to one of the following categories based on the number of leaflets present:
1. Unifoliate: A single leaflet is connected to the winged petiole in this form.Example Citrus
2. Bifoliate: The apex of the petiole develops two leaflets of this kind.Example Hardwicke
3. Trifoliate: This form develops three leaflets from the apex of the petiole.Example Aegle marmelosus
4. Quadrifoliate: – Four-leaf leaves emerge from the tip of the petiole in this form. Example Marseglia
5. Multifoliate: The tip of the petiole develops more than four leaflets in this form.Example Silk cotton
Modification of Leaves
Leaf modification refers to any change in the normal form and structure of a leaf or its parts in response to a plant’s need. The following leaf alterations are recognized based on the nature of Special functions:-
1. Leaf tendrils: Tendrils are long, slender, coiled structures that are sensitive to touch and can originate from any part of the plant and are used to climb. Tendril climbers are the name for such plants.
Example In Garden Pea, the terminal leaflet is transformed into a Tendril, in Gloriosa, the leaf tip is transformed into a Tendril, and in Smilax, the stipules are transformed into a Tendril.
2. Phyllode: A Phyllode is a green, flattened leaf-like modified petiole or Rachis used for photosynthetic structures when the Lamina is underdeveloped. Secondary Rachis and leaflets are lost during early growth in Acacia melanoxylon (Australian acacia), and the Petiole is converted into Phyllode.
3. Leaf Buds: Leaf buds are a type of accidental bud that forms on the surface of the leaf and is used for vegetative reproduction. Epiphyllous buds are another name for them. Leaf buds form along the margins of Bryophyllum, for example. They grow roots on the bottom and leaves on the top. This has the potential to become a self-contained plant.
4. Leaf Spines: A leaf-spine is a hard, pointed structure that develops from the leaf. Its purpose is to provide protection as well as to monitor perspiration. For example, the spines of the Opuntia leaf have been changed. Stipules are transformed into spines in Acacia, Date palm, Agave, and Yucca. The tip of the leaf is spiny in Date palm, Agave, and Yucca. The border of the lamina is spiny in Argimone.
5. Insectivorous plants: “Insectivorous plants” or “Carnivorous plants” are plants whose leaves have been adapted to capture insects to meet their nitrogen requirements.
1)The spoon-shaped Drosera Lamina is covered in sticky hairs called Tentacles that shimmer like dew in the sunlight. Insects mistook it for Nector and landed on it to feed. Sensitive tentacles bend over insects, trapping and digesting them using tentacle secretions.
2)In Nepenthes (Pitcher) complete Leaf is changed into a beautifully colored Pitcher, with a top to capture the Insects. The Pitcher’s inner wall is covered in hairs that prevent insects from escaping and secrete digestive enzymes that help it digest its protein. The Pitcher’s edge is a little slick. When an insect lands on a pitcher, it crawls inside and is digested.
3)Dionea muscipulata (Venus Fly Trap): It traps prey via trapping structures made by the margins of rosette leaves, which are equipped with tiny hair known as ‘Trigger hair.’ These are touch-sensitive. The lamina’s inner surface is brilliantly colored.
4) Utricularia (Bladderwort) is a submerged Hydrophyte with floating and submerged leaves. A Bladder with a Trap door is created from the floating leaf. It permits small aquatic insects to enter, then closes the trap door, imprisoning and digesting the bug to meet the nitrogen requirement.