Leaf

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.