Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Life habit: lichenized Thallus: thin, often inconspicuous, effuse or delimited by a blackish prothallus, usually forming small, neat patches, occasionally mosaic-forming surface: whitish or grayish, sometimes tinged olivaceous, smooth Ascomata: 0.5-2.2 x 0.1-0.2(-0.3) mm, usually numerous, simple or frequently branched, occasionally stellate, scattered or often contiguous, usually sessile, black, shiny; disc a slit, widening slightly when old, rarely opening, not pruinose exciple: closed, K+ olive-green hymenium: 30-50 µm tall, I+ blue turning quickly red; subhymenium: pale brown, 12-25 µm; epihymenium: brown or green-brown, K+ olive-green; paraphysoids: to 1 µm wide asci: clavate-subglobose, 32-40 x 10-14 µm (Calcarea-type) ascospores: 12-18(-20) x 3-4(-5) µm, 3-septate, ellipsoid or often ± clavate (Calcarea-type) Pycnidia: immersed conidia: 4-6 x 0.7-1 µm, straight or slightly curved, bacilliform Spot tests: thallus K-, KC-, C-, P-, UV- Secondary metabolites: none detected. Substrate and ecology: on smooth bark of young or old trees, more rarely on wood World distribution: holarctic in the Northern Hemisphere (throughout the United States according to Fink, 1935); also known from New Zealand Sonoran distribution: southern California, Baja California, and Sonora. Notes: This is one of the most common epiphytic species of the genus. It differs from the close O. erosa by the K+ olive-green exciple and asci of calcarea-type.