Pannaria is a genus of lichen-forming fungi in the family Pannariaceae. These lichens form leaf-like, scaly, or crusty patches that typically arrange themselves in loose rosettes on tree bark in humid forests. Most species partner with nitrogen-fixing cyanobacteria, though some contain green algae instead. The genus was established in 1828 and now includes about 80 recognized species found worldwide, particularly in tropical and subtropical regions.
Description
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 (hypothallus) 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 (pruina). 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 discs 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 photobiont cells. A thin, pale exciple of pseudoparenchymatous 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.
