Pannaria forms a
thallus that can be leaf-like (
foliose), a mosaic of tiny scales (
squamulose), or a thin crust (
crustose). Many species arrange their lobes in loose
rosettes and, unlike several related genera, they rarely develop the blue-black felt () seen beneath other
cyanobacterial lichens. The upper surface ranges from grey-blue to deep brown-black and may carry a light dusting of frost-like crystals (). Most species partner with the filamentous cyanobacterium
Nostoc, but members of the
Pannaria sphinctrina group instead contain
green algal cells. The lichen's sexual
fruiting bodies are sessile
apothecia whose red-brown to black are framed by a persistent rim of thallus tissue. That rim has two zones: an outer layer of tightly packed, brick-like cells and an inner layer that is looser and packed with cells. A thin, pale of cells surrounds the
hymenium. The
asci hold eight
ascospores, show no blue reaction to
potassium–iodide stain (K/I–) and lack the
amyloid plug found in many related
taxa. Their spores are colourless, single-celled,
ellipsoidal and often end in one or two small points; the outer wall is finely warted or ridged.
Asexual reproduction is limited to scattered
pycnidia that release straight, rod-shaped
conidia.
Thin-layer chromatography usually detects no
secondary metabolites, though some species contain
pannarin, which produces an orange-red colour with the
para-phenylenediamine (Pd)
spot test. ==Photobiont==