Phylogenetic analyses reveal that the Ostropomycetidae comprises two major evolutionary lineages: the Pertusariales-Icmadophilaceae clade and a group consisting of the Ostropales, Baeomycetales, and Hymeneliaceae.

[3] The Ostropomycetidae are a subclass of fungi that can exist either as non-lichenised forms or as lichens with a variety of body types, including crust-like, scaly (squamulos), or filamentous thalli.

[3] The reproductive structures (ascomata) of these fungi can be found embedded in the lichen's surface (immersed), sitting on top of it (sessile), or raised on a stalk (pedunculate).

[3] Inside the ascomata are special sac-like cells (asci), each typically holding eight or fewer spores (ascospores).

These spores are colourless and can be simple (without internal divisions), divided by transverse walls, or arranged into more complex, brick-like partitions (muriform).