Moisture and inorganic salts. Lichens are organisms of fungi and algae. The fungi absorb water and inorganic salts and supply them to the algae, while the algae supply the fungi with the products of photosynthesis. Lichens can be divided into three categories based on their external morphology: crustaceous lichens, leafy lichens and crystal lichens. In addition to the dense and sparse colorless fungal filaments that crisscross the body of the lichen, there is an algae layer in the middle, which is composed of algae cells. There are also bunches of false roots extending from the lower layer, which have no real roots, stems, leaves and other organs.