The sheet is a generally flattened vegetative organ of vascular plants , mainly specialized to perform photosynthesis . The morphology and anatomy of stems and leaves are closely related and together, both bodies are the stem of the plant . The typical leaves, the nomófilos , are not the only ones that develop during the life cycle of a plant because since the germination will occur different types of leaves - cotyledons , primary leaves, prophylls , bracts and antófilos in flower - shaped and very different functions. A nomófilo usually consists of a sheet flat, a short stalk, the petiole - connecting the blade to the stem and, at its base, a pair of leaf-like appendages, the stipules -. The presence or absence of these elements and the extreme diversity of forms of each of them has generated a rich vocabulary to categorize the types of leaves multiplidad presented by vascular plants and whose description is called leaf morphology . 1
In pteridophytes earliest leaves are small, have no vascular bundles and are called microphylls . Vascularized leaves, the megafilos or fronds , are characteristic of modern pteridophytes are more developed and have vascular bundles. 2 Many gymnosperms have a very characteristic type of leaf, the acicular leaf , which is a green needle plate, covered by a single vein and ending in a sharp point. 3 Most monocots have leaves with a distinctive look. Are usually whole with parallel venation, and the sheath is always well developed. 4 The dicotyledonous sheets usually have leaf lamina may be petiolate or sessile and the leaf base may be required or not. In this group of plants can be simple or compound leaves.
In the first case, the sheet can be whole, split or lobed, or sectada game. In the present case of compound leaf, the leaf is divided into several subunits called leaflets , which are articulated on the rachis of the leaf or divisions thereof. When more than three leaflets according to the disposal and take the same, the sheet can be pinnate when the subunits or leaflets are arranged along an axis or rachis. When the subunits or leaflets are inserted at the end of the spine are called leaves palmately . 5
The leaves may undergo structural changes pronounced, which may be considered, in most cases, such as adaptations to the environment , or the result of a specialized functional role other than that typical of this organ. These include leaves, reserving the cataphylls - specialized leaves as organs of support and fixing-the earrings - and leaves that carry out functions of defense-the leaf spines -.
The senescence leaf is a series of events organized and carefully controlled to allow plants to prepare for a period of rest and systematically extract the precious resources of the pages before them to die. 6 annuals in some of the leaves die prematurely while most of the leaves die while the remaining organs. In the trees , shrubs and herbaceous perennials , however, defoliation is a periodic phenomenon, very complex, which occurs in most species by a mechanism of abscission . 7 Leaves of many species show a good red differentiated in the fall, during this period, flavonols become colorless anthocyanins red when the chlorophyll of the leaves is degraded.
The leaves are typically needle-like lamellar structures or containing mostly photosynthetic tissues, located always at the light . In the leaves produces most of the perspiration , thereby leading to the suction that pulls water and inorganic nutrients from the roots . Additionally, the leaves can change its structure so as to function as storage organs of water . 9 10 In vascular plants the leaves are characteristically associated with buds that are in your armpits. These buds can grow into side branches vegetative or reproductive structures.