Leaf - Blade, Venation, Anatomy, Epidermis, Mesophyll, Veins, Phyllotaxy, Evolution - Morphology
leaves compound species petiole
A leaf is a plant organ which is an outgrowth of the stem, and has three main parts: the blade, a flattened terminal portion; the petiole, a basal stalk which connects the blade to the stem; and the stipules, small appendages at the base of the petiole. However, the leaves of many species lack one or more of these three parts.
Leaves function in photosynthesis, or the biological conversion of light energy into chemical energy; in transpiration, or the transport of water from the plant by evaporation; and in cellular respiration, the oxidation of foods, and consequent synthesis of high-energy molecules.
There is great variety of leaf size and shape among different species of plants. Duckweeds are tiny aquatic plants with leaves that are less than 1 millimeter in diameter, the smallest of any species of vascular plant. Certain species of palm tees have the largest known leaves, more than 60 ft (18 m) in length.
All leaves can be classified as simple or compound. A simple leaf has a single blade, whereas a compound leaf consists of two or more separate blades, each of which is termed as leaflet. Compound leaves may be palmately compound, in which the separate leaflets originate from one point on the petiole, or pinnately compound, in which the leaflets originate from different points along a central stalk which extends from the petiole.
Additional Topics
Venation is the pattern of veins in the blade of a leaf. The veins consist of vascular tissues which are important for the transport of food and water. Leaf veins connect the blade to the petiole, and lead from the petiole to the stem. The two primary vascular tissues in leaf veins are xylem, which is important for transport of water and soluble ions into the leaf, and phloem, which is important f…
Epidermal cells are on the upper and lower surfaces of a leaf. They have two features which prevent evaporative water loss: they are packed densely together and they are covered by a cuticle, a waxy layer secreted by the cells. The epidermis usually consists of a single layer of cells, although the specialized leaves of some desert plants have epidermal layers which are several cells thick. Epider…
Phyllotaxy is the arrangement of leaves on a stem. As a stem grows at its apex, new leaf buds form along the stem by a highly controlled developmental process. Depending on the species, the leaf origins on the stem may be opposite (in which leaves arise in pairs on opposite sides of the stem), whorled (three or more leaves arise from the same locus on the stem), or alternate (leaves are arranged i…
About 380 million years ago, plants with vascular tissue first evolved a special type of leaf, referred to as a microphyll. A microphyll typically has a single midvein, and arises from a stem which does not have leaf gaps, in regions of parenchyma (i.e, unspecialized) tissue where the vascular strand leads into the leaf base. The microphyll may have originated as an outgrowth of a vascularized ste…
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