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Fungi feed themselves quite ably, absorbing nutrients from organic materials. Algae and cyanobacteria are also adept at providing for their own nutritional needs by turning sunlight into energy through photosynthesis.
Yet many thousands of years ago, some fungi merged with some algae (or cyanobacteria in some cases) to create a new kind of partnership called a lichen.
Some 20,000 different kinds of lichens live in such diverse habitats as the surfaces of rocks in arctic tundra and desert sands as well as the bark of trees in bayous and the sides of buildings.
Lichen formation enables each of the partners to expand into habitats and environments they might not survive alone, such as wind-whipped tundra or sun-scorched desert.
Fungi provide the shelter and stability while the algae or cyanobacteria provide the food. The fungal filaments surround the algal or bacterial cells and make up the majority of the lichen’s bulk and shape. Meanwhile, the photosynthetic algae or bacteria churn out nutrients in the form of carbons, with up to 60% of what they produce being devoured by the fungal cells.
Lichens have an amazing capacity to withstand drought. Like very efficient sponges, lichens absorb moisture from fog, dew and even humid air. They can take in as much as 35 times their weight in water. They also retain water well, drying out very slowly. This ability enables them to survive in places like bare rock surfaces, deserts and tundra.
Some lichen partners are dependent upon one another for survival, but in many cases, the fungus and the algal or cyanobacterial species can each be found living independently.