Lichens are 'dual organisms' - a fungi and an algae in a stable, mutually beneficial (symbiotic) partnership. The fungus provides the structural form and protects the algae within from extremes of light and temperature. Algae are capable of photosynthesis and some of the sugars produced are released to provide the fungus with energy for growth and reproduction.
Lichen are capable of living for many hundreds of years and being sensitive to pollution levels they are important enviromental indicators.
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