Compound leaves are a characteristic of some families of higher plants. Each leaflet is attached to the rachis middle vein , but may have its own stalk. A palmately compound leaf has its leaflets radiating outwards from the end of the petiole, like fingers off the palm of a hand. Examples of plants with palmately compound leaves include poison ivy, the buckeye tree, or the familiar house plant Schefflera sp.
Pinnately compound leaves take their name from their feather-like appearance; the leaflets are arranged along the middle vein, as in rose leaves or the leaves of hickory, pecan, ash, or walnut trees.
In a pinnately compound leaf, the middle vein is called the midrib. Bipinnately compound or double compound leaves are twice divided; the leaflets are arranged along a secondary vein, which is one of several veins branching off the middle vein.
The silk tree Albizia is an example of a plant with bipinnate leaves. Leaves have many structures that prevent water loss, transport compounds, aid in gas exchange, and protect the plant as a whole.
The outermost layer of the leaf is the epidermis. It consists of the upper and lower epidermis, which are present on either side of the leaf. Botanists call the upper side the adaxial surface or adaxis and the lower side the abaxial surface or abaxis.
The epidermis aids in the regulation of gas exchange. It contains stomata, which are openings through which the exchange of gases takes place. Two guard cells surround each stoma, regulating its opening and closing. Guard cells are the only epidermal cells to contain chloroplasts. 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 avert 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.
Trichomes : Trichomes give leaves a fuzzy appearance as in this a sundew Drosera sp. Leaf trichomes include b branched trichomes on the leaf of Arabidopsis lyrata and c multibranched trichomes on a mature Quercus marilandica leaf.
The palisade parenchyma also called the palisade mesophyll aids in photosynthesis and has column-shaped, tightly-packed cells. It may be present in one, two, or three layers. Below the palisade parenchyma are loosely-arranged cells of an irregular shape.
Regina Bailey is a board-certified registered nurse, science writer and educator. Updated November 04, Key Takeaways Plant leaves are very important structures as they help to maintain life on earth by generating food sugars via photosynthesis. Leaves can have different shapes and sizes.
The basic components of leaves in flowering plants angiosperms include the blade, the petiole, and the stipules. There are three main tissues found in leaves: the epidermis, the mesophyll, as well as vascular tissue.
Each tissue type is composed of layers of cells. In addition to performing photosynthesis, some plants have other highly specialized functions. Examples include carnivorous plants that can 'eat' insects. Some animals, like the Indian leafwing butterfly, mimic leaves to camouflage themselves from predators. Featured Video. Cite this Article Format.
Bailey, Regina. Plant Leaves and Leaf Anatomy. Biology Prefixes and Suffixes: -phyll or -phyl. Forest Transpiration and the Water Cycle. The Structure and Function of a Cell Wall. The Structure of the Integumentary System. Your Privacy Rights. To change or withdraw your consent choices for ThoughtCo.
At any time, you can update your settings through the "EU Privacy" link at the bottom of any page. A plant is what the leave is attached to.
Stems hold up leaves to the light and keep fruits and flowers attached. They grow straight up, trail along the ground, climb fences and trees or stay underground. The Roots — the roots are the plants anchor and hold the plant firmly in the ground. Roots are also absorbers of water and minerals from the soil. They also store minerals. There is awesome variety in leaf structure and some may have all or few of the following parts. Small processes located to either side of the base of the petiole are called the stipule.
In some leaves there is no stipule for example. Nearly every leaf has a leaf stalk. The leaf stalk is called the petiole. The petiole attaches to the stem at a point called the leaf axil. 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 5. Figure 5. Trichomes give leaves a fuzzy appearance as in this a sundew Drosera sp.
Leaf trichomes include b branched trichomes on the leaf of Arabidopsis lyrata and c multibranched trichomes on a mature Quercus marilandica leaf. Wise; scale-bar data from Matt Russell. Figure 6. 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.
In the leaf drawing Figure 6a , the central mesophyll is sandwiched between an upper and lower epidermis. The mesophyll has two layers: an upper palisade layer comprised of tightly packed, columnar cells, and a lower spongy layer, comprised of loosely packed, irregularly shaped cells.
Stomata on the leaf underside allow gas exchange. A waxy cuticle covers all aerial surfaces of land plants to minimize water loss. These leaf layers are clearly visible in the scanning electron micrograph Figure 6b. The numerous small bumps in the palisade parenchyma cells are chloroplasts. Chloroplasts are also present in the spongy parenchyma, but are not as obvious.
The bumps protruding from the lower surface of the leave are glandular trichomes, which differ in structure from the stalked trichomes in Figure 5. Like the stem, the leaf contains vascular bundles composed of xylem and phloem Figure 7. 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. Figure 7. This scanning electron micrograph shows xylem and phloem in the leaf vascular bundle from the lyre-leaved sand cress Arabidopsis lyrata. 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.
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