Sunburst Lichen (Xanthoria elegans) on a rock in the Swiss Alps at an altitude of 2000 meters. Lichens are very unusual organisms. In a lichen a fungus lives in close symbiose with green algae and both partners benefit from each other. This cooperation enables lichens to live in habitats that can not be tolerated by any other organisms. They are always the first pioneer plants on bare rocks and stones.