Lichens are symbiotic colonies of fungi and algae. The fungus surrounds the alga and provides it with minerals and water absorbed from the atmosphere, and the alga in turn produces food for both. Lichens grow very slowly (about 1 cm/year) and can live in extreme environments for hundreds or even thousands of years. During droughts, they enter a stasis until water becomes available again. Lichens vary in texture and color depending on the type of fungus they contain and the amount of moisture available. Some fungi grow small but visible mushroom shapes that produce reproductive spores.
Common on rocks and trees in the Northern Highlands and on rocks in the Basalt Desert. In some areas of the Basalt Desert, the black basalt rocks are completely covered with contrasting white lichens.
Lichens are sensitive to pollution, making them an important indicator of environmental problems.