The venetian architecture of leaves varies greatly between and within species. Since a seminal study proposed a new integrative science of leaf venation there has been growing acknowledgement of the importance of leaf venation across plant biology and ecology. We wanted to introduce novice researchers to a wide range of classic and modern research, as well as to emphasise ideas that apply across organisational levels.

Leaf venation structure as a whole

Xylem and phloem cells are embedded in parenchyma, occasionally sclerenchyma, and surrounded by bundle sheath cells in veins. The phloem transfers sugars out of the leaf to the rest of the plant, whereas the vein xylem moves water from the petiole throughout the lamina mesophyll. The leaf venation systems of major plant lineages differ significantly, with many early groupings having dichotomously branching, open systems, while reticulation evolved frequently. Angiosperms have the most diverse vein structure, although they all share fundamental architectural aspects, such as a reticulate mesh formed by a hierarchy of vein orders (Lower-order veins are usually divided into three orders, known as major veins,’ which are typically ribbed with sclerenchyma .

From the petiole to the leaf apex, one or more first-order veins run, with second-order veins branching at intervals and third-order veins branching in between. Minor veins, which are found solely in angiosperms and consist of up to four orders of smaller, reticulate higher-order veins, can be distinguished from major veins. The timing of vein formation, as well as changes in gene expression during development, diameters and branching in mature leaves, and cross-sectional architecture, separate major and minor veins Haritatos A grid-like striate’ venation is common in multiple lineages, particularly monocotyledons, with several orders of longitudinal veins of various diameters and small transverse veins joining them (Ueno et al., 2006).

TYPES VENATION

Reticulate

1. a) Reticulate Pinnately    b) Reticulate Palmae

2.Parallel

1. a) Parallel Pinnates  b) Palmately Perpendicular

Venation is the arrangement of veins in the leaf blade or lamina. There are two forms of venation: reticulate venation and parallel venation.

Reticulate Venation: All dicot leaves have this sort of venation. There is a conspicuous vein termed the midrib in this style of venation, from which many minor veins emerge, eventually forming a net-like pattern in the lamina. There are two types of it.

Pinnately reticulate venation: There is only one midrib in the center of this type of venation, which forms many lateral branches to form a network. Mango, for example.

Parallel Venation

All of the veins in this sort of venation run parallel to one other. The venation of most monocot leaves is parallel. There are two types of it.

1. Pinnately,. There is a pronounced midrib in the center of this form of venation. Many veins emerge perpendicularly and run parallel to each other, as in the case of bananas.

1. Palmately parallel venation: This type of venation has multiple veins that emerge from the tip of the petiole and travel parallel to each other before coming together at the apex. They converge at the apex in grass, which is why it is called convergent. All of the main veins in Borassus (Palmyra) stretch out towards the perimeter. As a result, it is said to be divergent.

Leaves Modification

We already know that leaves are specialised for photosynthesis. They also have other important responsibilities to play, such as support, food storage, defense, and so on. They have been adjusted in various ways for each of these functions.

Pea tendrils, cactus spines, onion bulbs, insectivorous plant leaves, and other modified leaves are examples. Let’s take a closer look at some of the leaf modifications:

Storage Leaves

Plants that are xerophytic, such as those in the Crassulaceae family, have thick, succulent leaves that retain water in their tissues. Large vacuoles filled with hydrophilic colloid can be found in the parenchymatous cells of these leaves. This alteration aids the plant’s resistance to desiccation.

Tendrils of the leaves

Plants with weak stems have leaf tendrils. Tendrils are thread-like structures that develop from the leaves. These tendrils sustain the plant by climbing a neighbouring stick or wall. In Lathyrus aphaca, for example, the entire leaf is transformed into tendrils. Pisum sativum’s top leaflets are transformed into tendrils.

Spines of the leaves

Spines are needle-like features that have been adapted into the leaves of a few plants. The spines serve as defence mechanisms. They also cut down on water loss from perspiration. The leaves of Opuntia, for example, are transformed into spines.

Scale Leaves

These are thin, membrane structures with no stalks that seem brownish or colourless. They guard the auxiliary bud that grows in their axil. Onion scale leaves are meaty and thick, and they store both food and water. Sale leaves can also be found in Casuarina and Asparagus.

Hooks for leaflets

The terminal leaflets of some plants are transformed into hook-like features that aid in climbing. Bignonia unguis cati, for example.

Roots of the leaves

One of the leaves present at the nodes is transformed into adventitious roots in a few plants, allowing them to float above the water surface. Salvinia, for example.

Phyllode

The petiole of some plants flattens out and takes the shape of a leaf, turning green in colour. Phyllode is the term for this. Take, for example, Australian Acacia.

Insectivorous Leaves

Only a few plants require nitrogen to grow. The leaves of these plants have been engineered to trap and digest insects. The following are a few of the changes:

• Leaf Pitcher- The leaf lamina of a few plants, such as Nepenthes, is transformed into a pitcher-like structure. The insect is digested by the pitcher’s inner walls, which release a digestive fluid into the cavity.

• Leaf Bladder- In these plants, the leaf segments are transformed into bladders. These plants can be found in bodies of water. Digestive glands are located on the inner wall, which aid in the digestion of the trapped bug. Utricularia, for example.

• In Drosera, the lamina has many hairs at the tip of which is a sticky globule containing digesting enzymes. When an insect lands on the lamina, the hair totally envelops it.

Leaves’ Functions

The functions of the leaves are as follows:

Photosynthesis

The major function of leaves is photosynthesis. Photosynthesis is the process by which they transform carbon dioxide, water, and UV light into glucose.

Transpiration

The removal of surplus water from plants into the atmosphere is known as transpiration. The opening of stomata in the leaves causes this to happen.

Guttation

Guttation is the process of removing surplus water from the xylem at the edges of the leaves when the stomata are closed.

Storage

Photosynthesis takes place on the leaves. As a result, they conserve water and nutrients. The succulent, thick leaves are especially well-suited to water storage.

Defence

To prevent them from being harmed or devoured by animals, some leaves have been converted into spines. Opuntia, for example.

Conclusion

The photosynthetic pigment chlorophyll is found in the leaves, which are situated at the nodes of the stem.Leaf base, leaf lamina, and petiole are the three primary elements of a leaf.Simple leaves and compound leaves are the two types of leaves that exist. Leaves can also be acicular, linear, lanceolate, orbicular, elliptical, oblique, central cordate, and so forth.They are responsible for photosynthesis and aid in the elimination of excess water from the plant’s aerial portions.Spines, tendrils, hooks, and scales are added to them to assist them adapt to different habitats.