Lichens (IPA: /ˈlaɪkən/ or /lɪtʃ.ən/) are symbiotic associations of a fungus (the mycobiont) with a photosynthetic partner (the photobiont also known as the phycobiont) that can prouce food for the lichen from sunlight. The photobiont is usually either green alga or cyanobacterium. A few lichens are known to contain yellow-green algae or, in one case, a brown alga. Some lichens contain both green algae and cyanobacteria as photobionts; in these cases, the cyanobacteria symbiont component may specialize in fixing atmospheric nitrogen for metabolic use.