The fungal component of a lichen, the mycobionts of most lichens (98%) belong to the fungal Subdivision Ascomycotina (the "sac fungi"). Lichenization also occurs in a few members of the fungal Subdivisions Basidiomycotina (the "club fungi") and Deuteromycotina, as well as the enigmatic Geosiphon. Names given to lichens are considered as referring to the mycobiont.

The fungal component of the lichen partnership, absorbing nutrients and providing structural support for the plant.