One of the classic stories of biology, taught to virtually every student, is the fact that what we call “lichens” are actually a combination of two very distantly related species: a species of alga and a species of fungus. (Sometimes the “alga” is really a species of cyanobacteria, formerly called “blue green algae” but not really algae.) It is offered as the paradigm of a true symbiosis, in which two species living together each provide something for the other. In the case of lichens, the alga provides the products of photosynthesis as nutrients, while the fungus provides structure, protection, nutrients, and moisture. They’ve coevolved to the extent that while the algal partner can sometimes be found living freely on its own, the fungus is never found on its own. Finally, most (but not all) of the fungal partners in a lichen are ascomycetes (“sac fungi”)—a phylum in the fungal kingdom.
Lichens…
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