The evergreen plants comprise of leaves which are functional in more than one season while the leaves of deciduous plants will fall off every year. The leaf in general consists of two parts such as lamina or leaf blade that is expanded and the other part is leaf stalk or petiole. There are certain small outgrowths at the end of the petiole called stipules. The green part of the tissue in the leaf is lamina which is held strongly with a midrib and small veins.
There are four types of veins present in the leaves. They are parallel venation, reticulate venation, pinnate venation and palmate venation. In parallel venation, the veins are present parallel to one another. The veins here travel all along the length of leaves as seen in Eucharis grandiflora. Sometimes, the veins in parallel venation might start from midrib towards the margin as seen in grasses. In reticulate venation, the veins will form branching to create a network. Most of the dicots will have reticulate venation as in Viola species.
In pinnate venation, there is only one main midrib which gives rise to several small veins that branch off into many divisions. In palmate venation, many principal veins arise from the bottom of the leaf blade as seen in Carica papaya.
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