Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.

Thallus: 3-7 mm across, ± flat, monophyllous or marginally divided into rounded lobes, often closely appressed throughout; lobes 1-2 mm long, 0.5-1.5 mm wide; edges: turned downward and thickened on underside upper surface: smooth, white with slight greenish tinge, unchanged in herbarium, somewhat mealy-roughened, sometimes with narrow black edges in places lower surface: medium yellowish brown to orangish brown, to greenish black near edge; umbilicus distinct Apothecia: common, mostly marginal (and often projecting somewhat beyond main edge of thallus), long immersed, finally broadly sessile but appressed and scarcely constricted at the base, to 1.0 (-1.4) mm diam.; disc: plane to slightly convex, matt, ± dark or deep brown, usually with reddish or grayish tinges, somewhat pruinose; thalline margin: concolorous with thallus, to 0.1-0.2 mm wide, level with disc, entire to slightly flexuous, occasionally crenate towards outside, finally excluded; hymenium: 50-60 (-80) µm high, hyaline, the uppermost 10 µm inspersed with brownish granules; paraphyses it ascospores: oblong, often slightly to moderately curved, usually narrowed at one or both ends, (12-) 15-20 (-23) x (3-) 4-5 µm Pycnidia: occasional conidia: 20-30 µm long Spot tests: upper cortex: K-, C+ yellow, KC+ yellow, P-, UV-; medulla: K-, C-, KC-, P-, UV- Secondary metabolites: upper cortex: with pseudoplacodiolic acid; medulla: none detected. Substrate and ecology: on calcium poor siliceous rocks, apparently strongly nitrophilous, but growing in somewhat shaded areas World and Sonoran distribution: California and Baja California, c. 1300 m. Notes: This species is unlikely to be confused with any other lichen, except occasional small specimens of R. marginalis, from which it is easily separated especially by the elongated, curved spores.