When I am guiding a hike and I ask my group what this colorful stuff is on the rock, most people say it is moss. It is called lichen. Lichen is an organism that is made up of two independent organisms. One is fungus and the other is algae. They live together in a symbiotic relationship to help each other survive. Algae requires moisture to survive and fungus is very hardy and requires less water to survive. What little moisture the fungus needs can be acquired from the algae if external sources are not available. The fungus lives on the outside to protect the algae from evaporation and the algae lives safely between the fungus and the rocks.
Lichen is very hardy. It can live successfully on the poles of the earth, in the deserts, basically anywhere. Recently a French scientist sent lichen to space on the shuttle for an experiment. He exposed the lichen to raw space for 14 days and returned it to earth for examination. After being exposed to sub 200 degree temps, radiation from the sun and the absence of oxygen and water, the lichen was unchanged.
Some cultures use lichen for medicinal purposes, some use it for dyes. Some animals eat it. If the lichen is a bright color, it is poisonous.
There is a little story about lichen: "Freddy Fungus lived out in the forest. Alice Algae lived over by the creek. Well, one day they took a lichen to each other and decided to move in together even though they were living in syn-mbiosis. Eventually they did get married though, but now the marriage is on the rocks."