Lichens
A lichen consists of a fungus and an alga in symbiosis. The alga contain chlorophyll and can make chemicals needed for survival. The fungus shelters the alga, and determines the form of the lichen. Lichens have no roots: they absorb water and gases from their surfaces. They are therefore sensitive to pollution of the air. Lichens can grow on many different surfaces, according to species.
Lichen on stone
Lichen on wood
