Thallus: crustose, endolithic, evanescent and present only around the base of apothecia, or thin and rimose, plane surface: dark gray, dull; margin: indeterminate; prothallus: lacking; vegetative propagules: absent Apothecia: frequent, rarely contiguous, immersed in substrate or sessile, up to 0.35-0.5 mm in diam. disc: black, plane, often becoming convex or half-globose thalline margin: concolorous with thallus or partially concolorous with disc, 0.05-0.1 mm wide, entire, frequently becoming excluded; excipular ring: sometimes present, confluent thalline exciple: 60-110 µm wide laterally; cortex: absent or cellular, 10-20 µm wide; cells: up to 5.5-6.5 µm wide, pigmented; algal cells: up to 10-14.5 µm in diam.; thalline exciple: 50-120 µm wide below; cortex: not expanded proper exciple: hyaline, 10-15 µm wide, 20-40(-75) µm at periphery hymenium: 100-130 µm tall, inspersed or not; paraphyses: c. 2 µm wide, not conglutinate, with apices up to 5-6.5 µm in diam., heavily pigmented, forming a dark brown epihymenium; hypothecium: hyaline, 50-100 µm thick asci: clavate, 50-90 x 16-22 µm, 8-spored ascospores: brown, 1-septate, broadly ellipsoid, type A development, Bischoffii-type, (14.5-)16.5-18(-20) x (8-)10-11.5(-13) µm, lumina rounded at apices from start, broad canal sometimes becoming excluded, typically with broad pigmented band around septum; torus: absent; walls: not ornamented (Fig. 63) Pycnidia: immersed, pigmented ostiole protruding from thallus; conidiophores: Type VI conidia: sparsely produced, bacilliform, often with persistent attachment point, 3.5-5.5 x 1 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on limestone and calcareous sandstone World distribution: Europe from the Arctic Circle to North Africa, Asia, Australia and New Zealand and widespread in North America but absent from the northern Coastal Ranges, Cascades and Sierra Nevada Sonoran distribution: southern California and Arizona at elevations of 680-1860 m. Notes: The species is very variable with respect to external morphology, the thallus ranging from being relatively well developed with sessile apothecia to entirely endolithic with the apothecia immersed in the substrate. This latter morphotype usually has been treated as a separate species, R. immersa (Giralt 2001, Mayrhofer 1984, Mayrhofer and Moberg 2002), on the grounds that the hymenium also consistently lacks oil droplets. However, many examples of the bischoffii-morphotype with little or no inspersion, and also of the immersa-morphotype possessing some inspersion can be found, so the two forms intergrade in this respect. The two morphotypes sometimes are found side by side without intermediate forms. Sheard (1967) suggested that the different morphotypes are the result of different substrate textures, the form with immersed apothecia being found on softer substrates. Such differences in texture occur on adjacent parts of the substrate and the juxtaposed morphotypes therefore may be growing in different environments. It follows that the two morphotypes may not reflect different genotypes. Rinodina bischoffii is closely related to R. guzzinii, that differs in the better developed thallus, and significantly larger, and parallel sided spores.