The leaves of gymnosperms
There is a leaf shape typical of gymnosperms, the acicular leaf , present in Abies , Larix and Picea . Each leaf acicular has two parts, the sheet is a green needle, covered by a single vein and ending in a sharp point, and the base with the axis concrescente involving what is known as leaf bearing. On each of the faces of the sheet there are two longitudinal lines which indicate the location of the stoma . In Sequoia leaves show a slight dorsiventral flattening. The genus Pinus foliage has a particular, since it has two kinds of leaves: the long branches only have leaves reduced, applied against the stem. In the axils of these scales are inserted short branches, bearing at its base some scales and end in 1-5 needle-like leaves.
In families of taxodiáceas , Cupressaceae and Podocarpaceae leaves show way to scale and have a single nerve, while in some species of the family Araucariaceae leaves are broadly ovate and with several veins. In Ginkgoaceae leaf is fan-shaped, with expanded limbo dichotomous venation open. In the genus Cycas leaves are pinnately compound. In the cypress and Thuja leaves are small and concrescent, partially welded to the stem. Finally, in Gnetum sheets are similar to those of dicots.
The leaves of monocots exhibit morphological diversity almost as wide as those of dicots. However, most leaves have a common feature characteristic. They are usually entire, with parallel venation, and the sheath is always well developed. 4
A first type, exemplified in Zea mays , Tulipa and Convallaria presents limb entire, elongate, parallel venation, and is fixed to the stem by means of a sleeve which embraces more or less completely. At the junction of blade and sheath may have a laminar appendage called ligule , upright. The sheet has two faces well defined homologous faces of the lamina of the leaves of the dicotyledonous. The medium beam can be larger and be associated with a prominent rib. 4
Another type of sheet is presented in monocotyledonous Araceae , in which there is a petiole between the sheath and the blade. The water hyacinth is inflated petiole and leaf has a single stipule, membranous, located between leaf and stem. In Potamogeton leaves show a pair of stipules, one on each side, which may be partially welded to the sheet. The leaves of Marantaceae have pulvinos between the petiole and lamina, allowing them to change the position of the leaf blade horizontal (daytime) to vertical (night).
In Iridaceae presents a third type of leaf: leaves ensiformes or equitantes. The leaves have a sheath which carries on its dorsal face the limbus, arranged in a plane perpendicular to the surface of the stem. The first leaves show only subsequent pod and have increasingly developed their limbo. The limb is flattened, but both sides are vertical. In other cases the basal portion of the sheet is sheathing, and the apical portion of the lamina form, without a morphological difference between the two portions, as in Iris . An organization of the same type seen in the leaves of the onion and Juncus microcephalus , but with cylindrical sheath, cylindrical sheet fully closed and locked at the apex. The first leaves of the onion are like those of Iris , almost without foil, because it is reduced to a simple mass of chlorenchyma . 4
In the family of palm leaves can be sectadas. The pinnate venation can be as Acrocomia totai (mbocayá) Arecastrum romanzoffianum (pindó) and Butia yatay (yatai) or spanked as Copernicia alba (carandá) Trithrinax campestris (caranda-t). In Caryota leaf is doubly sectada. 4
In Canna (Canna edulis) and Musa (banana) leaves are pinnately-paralelinervadas. The middle line of the sheet is occupied by a set of parallel veins, very close together, and the peripheral veins are diverted at right angles along the blade, running through it as secondary veins parallel, independent. Tends to tear the sheet due to lack of marginal reinforcements.
Dicots usually have leaves with leaf blade, petiolate or sessile may be the leaf base and may be required or not. In this group of plants can be simple or compound leaves. In the first case, the blade may be entire, as in the case of Citrus and Ligustrum - cleft or lobed - Pelargonium - heading - Quercus robur - or sectada - Dahlia , Petroselinum -. 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. Each leaflet in turn, may have or be petiolules sessile. 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. In this case the sheets may be imparipinnada ( Fraxinus ) or paripinnada as present or not a terminal leaflet, respectively. Depending on how the sheet can be split: bipinnate, tripinnada, cuadripinnada. In such cases there rachis secondary, tertiary, etc., and the blade portions are called pinnules. When the subunits or leaflets are inserted at the end of the spine are called leaves palmately compound , the Lapacho and the club drunk are two examples. If the leaflets are divided, the arrangement of the foliólulos be pinnate. Bipalmadas sheets are not known or bipalmaticompuestas.
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