Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.
Thallus: irregular to orbicular, up to 2 cm diam., often confluent with other thalli forming a larger aggregate lobes: up to 1 mm wide, flat to convex, usually broadest and flattened at the tips, rarely longer than 5 mm, eciliate upper surface: white to grayish, often with a darker zone near lobe tips, weakly maculate and usually shiny, sometimes with a white pruina; soredia and isidia absent upper cortex: paraplectenchymatous medulla: white lower cortex: pale, prosoplectenchymatous lower surface: white with a rose tinge; rhizines: concolorous, few and scattered Apothecia: abundant, up to 2 mm; margins: with thick, crenulate ascospores: brown, 1-septate, Physcia to Pachysporaria type, 15-18 x 7.5-8.5 µm Pycnidia: common, immersed conidia: subcylindrical, 4-6 x 1 µm Spot tests: upper cortex K+ yellow, C-, KC-, P+ yellow; medulla K-, C-, KC-, P- Secondary metabolite: upper cortex with atranorin. Substrate and ecology: growing on open rocks World distribution: known only from a limited area near Cuzco in southern Peru and SW North America Sonoran distribution: known only from a few montane localities from Baja California Sur, Chihuahua, Sonora and Sinaloa. Notes: The small size, the ± convex lobes, the presence of apothecia, the lack of soredia and the K medulla are the main characters of P. convexella. It might be the fertile counterpart of P. nashii. The corticolous P. stellaris is keyed out with P. convexella as both have K medulla. They are, however, in addition to different substrate preference, easily separated by their different lobe shape; truncate in P. convexella and rounded in P. stellaris.