About 40 genera of algae and cyanobacteria are found in lichen partnerships. They also provide vitamins to the fungus. Cyanobacteria can make amino acids directly from the nitrogen gas in the atmosphere, something neither fungi nor algae can do. The fungus, in turn, protects its partners from drying out and shades them from strong sunlight by enclosing the photosynthesizing partners within the body of the lichen. This life habit has allowed lichens to successfully colonize many different habitats.
Lichens have a truly remarkable resistance to drought.
Lichens can also absorb moisture from dew or fog, even from the air itself if the humidity is very high and the temperature is low. This ability to quickly absorb and retain water from many sources makes it possible for lichens to live in harsh environments like deserts and polar regions, and on exposed surfaces like bare rocks, roofs and tree branches. Foliose Crustose Fruticose Ssquamulose Most lichens grow slowly, probably because they live in environments where water is available for only short periods. They tend to live for many years, and lichens hundred of years old can be used to date the rock surfaces on which they grow. Lichens spread mostly by small pieces of their body being blown around.