Leaf classification

Structure of the leaves

In plants, the leaves represent a very important organ that deals with chlorophyll photosynthesis. They are usually flat in order to optimally increase the surface exposed to sunlight. The leaves are used for breathing, for transpiration and for guttation (elimination of water). The elements that make up the leaf are four (although almost always only some of them are present): the sheath, the stipules, the petiole and the lamina. The tissues are also very important: the epidermis, above and below the leaf which is often made impermeable by a substance called the cuticle; the mesophyll, which is formed by two parenchyma; the cribro-vascular bundles, whose function is to transport liquids; the stomata, openings that release the vapor and let in oxygen and carbon dioxide.

Leaf classification

Based on the shape of the lamina it is possible to distinguish between two-sided, equifacial and single-sided leaves. Bifacial leaves: they have a different upper and lower side (often present in dicotyledons). Equifacial leaves: they are the same in the upper and lower part (often present in monocotyledons). Unifacial leaves: they show only one face, folding on themselves and assuming a tubular shape, as in the onion. The leaves of conifers are called needle-like. Another classification is based on stomata, whose function is to release steam and let in oxygen and carbon dioxide. Hypostomatic leaves: stomata are in the lower part, epistomatic if the stomata are in the upper part, as in the case of the water lily,

Classification of the leaves according to the elements that compose them

There are multiple methodologies to classify leaves based on the characteristics of the parts that compose them, such as the base, the ribs, the margin and the lamina. The base, for example, can be corded, acute, obtuse, wedge-shaped, kidney-shaped, truncated, asymmetrical or irregular. The ribs can be pinnate (when scattered), parallel, curved (in the final stroke) or branched. A further method of leaf classificationit is based on the conformation of their margin, which can be smooth, wavy, serrated, doubly toothed, toothed-thorny, serrated, crenate, lobed, split, septate, snag. On the other hand, as regards the classification based on the shape of the lamina, we can have, for example, an elliptical, ovate, obovate, lanceolate, rhomboid, heart-shaped leaf.

Other classifications of leaves

There are further methods of classifying leaves, which for example are based on the characteristics of the petiole, their color and their surface. Relative to the petiole, it may or may not be present: in the first case the leaf is pedunculated, in the second case it is defined sessile. The petiole can be flattened in shape, with stipules (small leaves positioned at the base). When the leaf has a sheath that wraps around the stem, it is defined as a sheath. If the leaves have the same color on both pages they are called concolors while if the color they have is different they are called dicholors. The leaf surface can be leathery (thick), tomentose (velvety) or rough (rough) when it has a considerable amount of hair.

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