Lichens

Lichens are a particularly unusual life form. Each lichen, in fact, is a composite body formed by two distinct species, a fungus and a unicellular alga, whose cells are "mixed" neatly producing an original biological structure. Both species benefit from the presence of the other: the fungus receives nourishment from the photosynthetic activity of the alga, while the latter takes advantage of the mechanical protection offered by the fungus, as well as of its ability to retain moisture.