They grow tightly pressed against their rock surface, occasionally resembling crust-like lichens due to their closely adhering thalli.

The lobe-shaped "leaves" are slightly rounded, flattened from top to bottom, and have a protective layer (cortex) on both their upper and lower surfaces.

Both the top and bottom cortical layers are formed of fungal filaments aligned perpendicularly to the surface and show no notable colour changes with common chemical tests (K–, N–).

[4] Allantoparmelia also produces tiny, embedded structures called pycnidia that release minute, colourless, elongated spores (conidia) that may be slightly club-shaped.

[4] Unlike related genera such as Hypogymnia and Brodoa, Allantoparmelia does not contain the common compound atranorin in its upper cortex, and it also differs in its tightly adhering growth habit and lack of rhizines.