The Ostropomycetidae are a subclass of mostly lichen-forming fungi in the class Lecanoromycetes. The subclass was circumscribed in 2004 by Catherine Reeb, François M. Lutzoni, and Claude Roux.[1] It contains ten orders and 36 families.[2]
Arctomiaceae is the only family in the Ostropomycetidae that associates with cyanobacteria of the order Nostocales as its main photobiont partner.[3]