Usnic acid was identified in many genera of lichens including Usnea, Cladonia, Hypotrachyna, Lecanora, Ramalina, Evernia, Parmelia and Alectoria. Although it is generally believed that usnic acid is exclusively restricted to lichens, in a few unconfirmed isolated cases the compound was found in kombucha tea and non-lichenized ascomycetes.
Usnic acid has been identified in numerous lichen species, including Usnea, Cladonia, Hypotrachyna, Lecanora, Ramalina, Evernia, Parmelia, and Alectoria. While it is commonly associated with lichens, there have been rare instances where the compound has been found in kombucha tea and certain non-lichenized ascomycetes.