Leaf, in botany, any usually flattened green outgrowth from the stem of a vascular plant. Although photosynthesis typically only occurs on the upper surface of the leaf, it can occur on both sides in some plant species. A compound leaf has two or more blades attached to the petiole. Leaves are initiated in the apical bud (growing tip of a stem) along with the tissues of the stem itself. Teardrop-shaped, stem attaches to the tapering end; reversed ovate. Leaf margins of simple leaves may be lobed in one of two patterns, pinnate or palmate. The mesophyll (also called chlorenchyma) inside the leaf that is rich in chloroplasts 3. Leaf Arrangement (Phyllotaxy) Three different leaf arrangements: Alternate (one leaf per node), opposite (two leaves per node) and whorled (three or more leaves per node). In perennial plants, leaf fall is usually associated with approaching winter dormancy. Having lobes with incisions that extend almost up, but not quite to the petiole. Veins, which support the lamina and transport materials to and from the leaf tissues, radiate through the lamina from the petiole. There are some indications that day length may control leaf senescence in deciduous trees through its effect on hormone metabolism; both gibberellins and auxins have been shown to retard leaf fall and to preserve the greenness of leaves under the short-day conditions of autumn. The first year is spent growing leaves, stems and roots. : a leaf whose blade is not divided to the midrib even though lobed â compare compound leaf. With the leaf blade surrounding the stem such that the stem appears to pass through the leaf. In descriptions of multiple leaves, the neuter plural is used, e.g. Opposite: show all. The oxygen liberated from green leaves replaces the oxygen removed from the atmosphere by plant and animal respiration and by combustion. Definition of a Leaf 2. leaf your worries behind; leaves abound from all around; leaves are falling, autumn is calling; leaves of red and gold; leaves will fall in fall; lovely leaves; oh my gourd! Leaves or leaf parts may be modified to provide support. Being divided by clefts, may be pinnately lobed or palmately lobed. Leaves are attached to the stem singly, ascending either on alternate sides of the stalk, or in a spiraling pattern. Plants that use insects as a nitrogen source tend to grow in nitrogen-deficient soils. A local concentration of cell divisions marks the very...…. Leaves may be simple, with a single leaf blade, or compound, with several leaflets. Leaves are the original solar panels, capturing energy from sunlight in a biochemical process called photosynthesis. When only a single blade is inserted directly on the petiole, the leaf is called simple. The major tissue systems present are: 1. Fiddle-shaped; obovate with a constriction near the middle. Leaf. The leaves are obovate, deciduous and up to 20 cm (7.9 in) long. Compound Leaf . As much as one-fifth of the mesophyll is composed of chlorophyll-containing chloroplasts, which absorb sunlight and, in conjunction with certain enzymes, use the radiant energy in decomposing water into its elements, hydrogen and oxygen. Spear-shaped: Pointed, with barbs, shaped like a spear point, with flaring pointed lobes at the base. Examples include, but are not limited to, Viburnums, Olive trees, Maple trees, Fringe trees, and Ash tree leaves. Alternate: show all. The Description of Leaves, University of Rochester, https://en.wikipedia.org/w/index.php?title=Glossary_of_leaf_morphology&oldid=982175207, Short description with empty Wikidata description, Creative Commons Attribution-ShareAlike License, Having two leaflets, each leaflet being bifoliolate, With three components, each with three leaflets, Consisting of leaflets all radiating from one point, Having two rows of leaflets on opposite sides of a central axis, see, Leaf blade in one continuous section, without leaflets (not compound), Pinnately compound in which each leaflet is itself bipinnate. 4.13). Triangular, wedge-shaped, stem attaches to point. The margins of simple leaves may be entire and smooth or they may be lobed in various ways. These layers protect the leaf from insects, bacteria, and other pests. The petiole sometimes extends into the leaf and divides the leaf into two equal halves, and when it does itâs called the midrib. A leaf is an above-ground plant organ and it is green. Gelatinous interior of the leaves of aloe (, Pitcher-shaped leaves of the carnivorous slender pitcher plant (. Many monocotyledons have sheathing leaf bases that are concentrically arranged and form a pseudotrunk, as in banana (Musa). Having lobes with incisions that extend less than half-way toward the midrib. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. Viscid (Viscous): Covered with sticky or resinous secretion. Various authors or field workers might come to incompatible conclusions, or might try to compromise by qualifying terms so vaguely that a description of a particular plant practically loses its value. Most leaves have a broad, flat part called a blade. It is highly recommended for planting in urban and suburban areas. Its main functions are photosynthesis and gas exchange. Leaves may also be folded or rolled in various ways. For example, whether to call leaves on the same tree "acuminate", "lanceolate", or "linear" could depend on individual judgement, or which part of the tree one collected them from. A tree leaf has several types of veins. foliis ovatis 'with ovate leaves'.. Having lobes with incisions that extend almost, or up to midrib. With a single leaflet. In the flame lily (Gloriosa superba), the leaf tip of the blade elongates into a tendril and twines around other plants for support. In the garden pea (Pisum sativum), the terminal leaflet of the compound leaf develops as a tendril. Ending abruptly in a small sharp point as a continuation of the midrib. Leaves of most plants include a flat structure called the blade or lamina, but not all leaves are flat, some are cylindrical. Carnelian is an alteration of cornelian that is based on Latin carn-, meaning "flesh," in reference to the flesh-red color that some perceive in the mineral. Carnivorous plants use their highly modified leaves to attract and trap insects. In many epiphytic bromeliads, the pseudotrunk also functions as a water reservoir. Abscission layers may also form when leaves are seriously damaged by insects, disease, or drought. The epidermis also secretes a waxy substance called the cuticle. Pinnately Compound . A leaf is made of many layers that are sandwiched between two layers of tough skin cells (called the epidermis). Their nervations come from the center of the leaf and often have a serrated base. Typically, a leaf consists of a broad expanded blade (the lamina), attached to the plant stem by a stalklike petiole. Leaf margins (edges) are frequently used in visual plant identification because they are usually consistent within a species or group of species, and are an easy characteristic to observe. Chlorophyll production in deciduous plants slows as the days get shorter and cooler, and eventually the pigment is broken down completely. 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