The leaf is one of the main parts of the plant, occupies a lateral position on the stem and photosynthesize, transpiration (evaporation of water by the plant), and gas exchange with the environment.
The leaves of the plants are very different according to their shape and internal structure, but almost always one can distinguish the leaf blade, petiole and base in them with which the leaf is attached to the stem.
The leaf emerged up two times in its evolution. An enamel leaf showed up in the Devonian, also called the phyloid and microfila. Firstly, it merged as a scaly appearance on the shoot, which served to increase the area of the photosynthetic surface. This outgrowth had to be supplied with water and taken from it by photosynthesis products, so a penetrating system attached into it. Now, such leaves are special attribute of the placenta and psilotoid. The leaf trace of the microfilae participates the stela without the formation of leaf lacunae. It stays in the apical meristem. The second time the macrophyll showed up on a stem. It arose on the basis of a group of telomes, which is located in the same plane, which flattened and fused. This kind of leaf is characteristic of horsetails, ferns, gymnosperms and flowering. There is also a belief that an enation is a reduction of macrophylls.