Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Thallus: squamulose, mostly (1-)3-6 mm across squamules: dispersed or contiguous, sometimes overlapping, 1 mm thick, regularly dividing upper surface: light to dark brown, but young squamules often whitish gray, dull, smooth but developing creases, sometimes blackening toward rims, epruinose cortex: prosoplectenchymatous, without surface formed of expanded hyphae apices, 90-120 µm thick; syncortex: thin, uneven, 10 µm thick; eucortex: obscure in water, 80-100 µm thick; upper layer: thin, reddish brown; lower layer: hyaline, prosoplectenchymatous, derived from hyphae from medulla interrupting algal layer algal layer: 150-200 µm thick, upper and lower strata uneven, interrupted with hyphal bundles medulla: prosoplectenchymatous, 100+ µm thick lower surface: reddish brown, darkening sometimes to black, but sometimes appearing white, corticate, formed from medullary prosoplectenchyma forming an anticlinal hyaline zone 30-40 µm thick, the outer surface formed from tightly packed apices in pigment hoods attachment: stipe Apothecia: punctiform, 0.1-0.2 µm wide, easily mistaken for pycnidia, pale brown, up to twenty per squamule disc: brown, slightly darker than thallus parathecium: indistinct epihymenium: hyaline, packed together in narrowed disc, 15-25 µm thick hymenium: hyaline, 190-210(-250) µm tall; paraphyses: c. 1 µm wide, thin-walled, with hyaline apices subhymenium: 30-35 µm thick, KI+ blue asci: narrowly clavate to cylindrical, 180-200 x 18-20 µm, 200+-spored ascospores: hyaline, simple, narrowly ellipsoid, mostly c. 5 x c. 1 µm Pycnidia: not observed Spot tests: UV-, all spot tests negative Secondary metabolites: none detected. Substrate and ecology: on granite and sandstone, often with Aspicilia species, usually above 1600 m World distribution: North America (Ohio and California) Sonoran distribution: southern California (Santa Monica, San Gabriel, and San Jacinto Mountains). Notes: Acarospora oreophila is often sterile. No pycnidium has been observed yet; just numerous nascent ascomata that may be easily mistaken for pycnidia. A number of species have narrower discs than the width of ascomata at mid-hymenium level, but this is most extreme reduction the author has seen so far. The ascus stains in the same way as other members of the genus. The species is successional, occurring on granite or sandstone, usually with or on Aspicilia species that usually pioneered the substrate. It may be a juvenile parasite on Aspicilia. The specimen from Ohio is much reduced, sterile, and suffering from a fungal infection. This disjunctive occurrence is indicative of a wider distribution, at least in the past.