A leaf (plural leaves) is the principal lateral appendage of the vascular plant stem,^[1] usually borne above ground and specialized for photosynthesis. In most leaves, the primary photosynthetic tissue, the palisade mesophyll, is located on the upper side of the blade or lamina of the leaf . Leaves are mostly green in color due to the presence of a compound called chlorophyll that is essential for photosynthesis as it absorbs light energy from the sun. A leaf with white patches or edges is called a variegated leaf.

The function of leaf in the plant.

All leaves have the same basic structure - a midrib, an edge, veins, and a petiole. The main function of a leaf is to carry out photosynthesis, which provides the plant with the food it needs to survive.

Photosynthesis

The primary function of the leaf is the conversion of carbon dioxide, water, and UV light into sugar via photosynthesis. The simple sugars formed via photosynthesis are later processed into various macromolecules required for the formation of the plant cell wall and other structures. Therefore, the leaf must be highly specialized to combine the carbon dioxide, water, and UV light for this process. Leaves are orientated to ensure maximal exposure to sunlight and are typically thin and flat in shape to allow sunlight to penetrate the leaf to reach the chloroplasts, which are specialized organelles that perform photosynthesis. Once sugar is formed from photosynthesis, the leaves function to transport it down the plant via specialized structures called the phloem, which runs in parallel to the xylem. The sugar is typically transported to the roots and shoots of the plant, to support growth.

Transpiration

Transpiration refers to the movement of water through the plant, and subsequent evaporation via the leaves. When the stomata open to accommodate the diffusion of carbon dioxide into the plant for photosynthesis, water flows out. This process also serves to cool the plant via evaporation of the water from the leaf, as well as regulate the plant’s osmotic pressure.

Guttation

Guttation refers to the excretion of xylem from the edges of leaves and other vascular plants due to increased levels of water in the soil at night when the stomata are closed. The pressure caused at the roots results in the leakage of water from the xylem out of specialized water glands at the edges of leaves.

Storage

Leaves are a primary site of water and energy storage since they provide the site of photosynthesis. Succulents are particularly adept at water storage, as evidenced by the thick leaves. Due to the high levels of nutrients and water, many animal species ingest the leaves of plants as a source of food.

Defense

Some leaves have also evolved defense mechanisms to avoid being eaten or damaged. Some examples include the spines of cacti, cones of gymnosperms, respectively. Moreover, the waxy coatings found on leaves serve to protect against water loss, rain, and forms of contamination. Oils and other secreted substances also detract from being consumed by herbivores.

Types of Leaf

Conifer Leaf

Conifer leaves are needle-shaped or in the form of scales. Conifer leaves are typically heavily waxed and highly adapted to colder climates, arranged to dispel snow, and resist freezing temperatures. Some examples include Douglas firs and spruce trees. The images below illustrate this type of leaf.

Microphyll Leaf

Microphyll leaves are characterized by a single vein that is unbranched. Although this type of leaf is abundant in the fossil record, few plants exhibit this type of leaf today. Some examples include horsetails and clubmosses. The image below illustrates this type of leaf.

Megaphyll Leaf

Megaphyll leaves are characterized by multiple veins that can be highly branched. Megaphyll leaves are broad and flat, and generally comprise the foliage of most plant species. The image below illustrates this type of leaf.

Angiosperm Leaf

Angiosperm leaves are those found on flowering plants. These leaves are characterized by stipules, a lamina, and a petiole. The illustration below shows an example of angiosperm leaves.

Fronds

Fronds are large, divided leaves characteristic of ferns and palms. The blades can be singular or divided into branches. The image below presents an example of a frond.

Sheath Leaf

Sheath leaves are typical of grass species and monocots. Thus, the leaves are long and narrow, with a sheathing surrounding the stem at the base. Moreover, the vein structure is striated and each node contains only one leaf. The image below presents an example of a sheath leaf.

Different Parts of a Leaf

Petiole

It is the stalk that connects a leaf to the stem of the plant, it is made of complex conducting tissues called vascular tissues.

Functions Providing support to the leaf and keep it erect
Transporting water and nutrients absorbed by the roots to the leaves
Transporting photosynthetic products from the leaves to the rest of the plant

Leaf Base

It is the lowermost part of a leaf, which is closest to the petiole.

Functions Helping in the attachment of the leaf to the stem
It protects the young axillary bud

Leaf-blade or Lamina

It is the thin, flat part of the leaf that is typically green in color. It is further divided into three parts: i) leaf apex – the tip of the leaf blade, ii) leaf margin – the edge of the leaf and, iii) leaf veins – the small channels or capillaries, which are further subdivided into venules.

Helping plants to prepare their food using raw materials like water, carbon dioxide, and minerals through photosynthesis.
Performing evaporation from the aerial parts of a plant by a process known as transpiration.

Axil

The angle between the upper side of the stem and a leaf, branch, or petiole. axillary bud - a bud that develops in the axil. Most leaves are flat and contain chloroplasts; their main function is to convert energy from sunlight into chemical energy (food) through photosynthesis.

Stem

Stem, in botany, the plant axis that bears buds and shoots with leaves and, at its basal end, roots. The stem conducts water, minerals, and food to other parts of the plant; it may also store food, and green stems themselves produce food.

Vein

The veins are the vascular tissue of the leaf and are located in the spongy layer of the mesophyll. The pattern of the veins is called venation. Cells that bring water and minerals from the roots into the leaf.

Tip

The flattened part of the leaf is the leaf blade or lamina, which can be subdivided into three discrete regions: The tip or apex is the part of the lamina farthest removed from the point of attachment of the leaf to the stem. The margin is the perimeter of the leaf between the apex and base.

Margin

The leaf margin is the boundary area extending along the edge of the leaf. There are lots of different types of leaf margins that are important for plant identification. While leaves on a single tree may differ in size, they will all have the same general shape and margin.

Midrib

The central vein, or rib, of a leaf, usually running from the stem to the apex. The central or main vein of a leaf, as in eudicots, magnoliids, and ferns. The strengthened vein down the middle of a flower petal or leaf.

Leaves We Eat

Spinach

Garden spinach is an annual plant that grows in temperate climates.The spinach you eat at home consists of these exact leaves before they reached their flower state.

Spinach leaves are especially suitable for people suffering from anemia.

For medicinal purposes and faster effect, it is preferable to take squeezed fresh spinach juice mixed with carrot juice.

The low caloric content of spinach makes it an extremely suitable dietary food.

Lettuce

It turns out to be especially valuable in the spring when our body is in great need of vitamins.It has been found that the outer, darker green leaves of lettuce contain much more carotene and vitamin C than the inner, lighter leaves. Chefs advise chopping the lettuce into pieces and season immediately before consumption with vinegar and olive oil.

Lettuce provides water to the body.
Lettuce improves the condition of the skin and hair.
Lettuce is ideal for dieting.
Lettuce helps with insomnia.

Microgreens

Microgreens are vegetables and herbs grown from seed and harvested at the seedling stage. These small plants have a great, bold taste. And it is this aroma that attracts chefs to microgreens and more and more restaurants in the USA grow microgreens in their lounges, in front of the customers. It is actually becoming a growing trend.

Boosting the immune system
Preventing cancer
Decreasing the risk of heart disease

Chard

Chard is a leafy vegetable common in Mediterranean cuisine. It is especially popular in Italian food, including risotto and pizza.

Lowering blood pressure
Fighting cancer
Protecting against osteoporosis

Kale

This vegetable belongs to the family of broccoli, cabbage, cauliflower. Its color is green and has a pleasant taste. An interesting fact about it is that it can be grown in areas with higher pollution.

Fighting cancer cells
Preventing obesity
Preventing osteoporosis

Arugula

Arugula was known thousands of years ago in Ancient Rome, where it was used as a spice. Even then, the seeds of the plant were considered an aphrodisiac.