Life habit: lichenized Thallus: thin, sometimes inconspicuous or immersed, smooth, continuous to rimose surface: whitish, ash-gray, brown or dull olive-green Ascomata: 0.5-2.5(-3.5) x (0.15-)0.2-0.3(-0.4) mm, numerous, sessile, mostly scattered, simple or infrequently branched, occasionally green-pruinose; disc a slit or becoming ± fully exposed exciple: closed, dark brown, K- hymenium: 60-90 µm, I+ reddish. epihymenium: brown or red-brown, K- or ± red-brown; hypothecium: pale brown, 15-50 µm, I+ red; paraphysoids: to 1.5 µm wide asci: claviform, 50-70 x 15-20 µm (Varia-type) ascospores: ellipsoid to fusiform, 18-28 x (4-)5-8 µm, 3-septate, straight or slightly curved, colorless, becoming ± red-brown when over-mature; wall not swollen at septa (Subelevata-type); perispore 0.5-1.5 µm wide Pycnidia: rare, immersed, punctiform conidia: 4-7 x 1 µm, bacilliform, straight Spot tests: thallus K-, C-, KC-, P- Secondary metabolites: none detected. Substrate and ecology: on acid to basic bark or on rock, also on wood or dead herbs; on usually smooth bark of Cupressus macrocarpa, Heteromeles arbutifolia, Quercus agrifolia, Q. pacifica, Q. tomentella and Umbellularia, and various shrubs in the Sonoran Region; when on rock, in ombrophobous communities, often with Dirina paradoxa subsp. approximata and Lecanographa hypothallina World distribution: widely distributed in the Northern Hemisphere, including Europe and North America (west coast) and also Australia Sonoran distribution: coastal, Baja California and southern California. Notes: Opegrapha herbarum is one of the most frequently collected species of the genus in the Sonoran region. Opegrapha saxicola Ach. was reported from California (Herre 1907, 1910; Fink 1935) but the material identified by Herre and present in the F herbarium corresponds to saxicolous O. herbarum.