Lichen land pioneers spread. Hardy and long-lived (some reach 9000 years of age), these low-lying photosynthesizers are an arresting example of symbiosis.
Just as bacteria and protoctist mergers led to algae, lichens represent a merger of fungi with photosynthesizers (algae and/or cyanobacteria). An entirely new life form, lichens enjoy the algae's ability to use solar power to make food and the fungi's ability to store water and protect themselves from the elements.
Through rock weathering, lichens play a significant role in the geological cycle. Crustose lichens produce acids which chemically decompose rocky substrates; lichens manufacture a variety of acids depending upon the nature of the rock. Lichens also produce a glory of pigments. We still do not understand how or why.