Thallus: crustose, thin, rimose, becoming rimose-areolate or areolate, areoles up to 0.3-0.6 mm wide, plane surface: light to dark gray or ochraceous, dull; margin: determinate or indeterminate; prothallus: lacking; vegetative propagules: absent Apothecia: sometimes erumpent, adnate, frequent but rarely contiguous, up to 0.35-0.6 mm in diam. disc: black, or reddish brown when wet, plane thalline margin: concolorous with thallus, frequently becoming carbonized and concolorous with disc, up to 0.05-0.1 mm wide, entire and persistent; excipular ring: lacking thalline exciple: 40-60 µm wide; cortex: 10-20 µm wide; cells: up to c. 4 µm wide, pigmented or not; algal cells: up to 9-12.5 µm in diam.; or thalline exciple: becoming partly or fully carbonized, 30-70 µm wide proper exciple: hyaline, c. 10 µm wide, expanding to c. 30 µm wide at periphery, often with aeruginose pigment, K+ red hymenium: 80-100 µm tall; paraphyses: 2-3 µm wide, sometimes conglutinate, with apices up to 4.5-6.5 µm wide, lightly pigmented, forming a light brown epihymenium; hypothecium: hyaline, 40-100 µm thick asci: clavate, 50-70 x 17-27 µm, 8-spored ascospores: brown, 1-septate, broadly ellipsoid, type A development, Mischoblastia-type, (15-)18.5-20(23) x (7.5-)10-11.5(-14) µm, mature spores sometimes inflated at septum, not more so in K; torus: narrow, in mature spores only; walls: lightly pigmented, usually very faintly pitted (Fig. x2) Pycnidia: immersed in thallus conidia: bacilliform 4-5 x 1-1.5 µm Spot tests: K+ yellow, C-, KC-, P+ faintly yellow Secondary metabolites: atranorin in cortex. Substrate and ecology: mainly on siliceous rocks, occasionally on basalt and rhyolite, rarely on soil World distribution: scattered in southern Scandinavia, central and western Europe, rare in southern Europe, also from southern Africa, Asia and Australia, widespread in eastern and southwestern North America Sonoran distribution: widespread in southern California and Arizona from sea level to 1585 m, Baja California Sur, Sonora, and Sinaloa. Notes: Rinodina oxydata is characterized by its Mischoblastia-type spores and thallus with atranorin in the cortex. The apothecia often become lecideine in appearance when the thalline margin becomes carbonized and the algae lost, making the species easily identifiable in this state. Some specimens from California, growing on soil and loosely compacted conglomerate, possess significantly larger spores (averaging 24.5-26.5 x 12.5-14 µm), with a well-developed torus and more strongly pitted walls. They may prove to belong to a separate species.