Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.
Thallus: crustose, usually thin but thick on protected parts of substrate, comprised of scattered, irregular areoles, c. 0.4 mm wide, becoming contiguous, up to 0.6-1.1 mm wide, plane to rugose surface: dark gray to brownish gray, brown when moist, dull; margin: indeterminate; prothallus: lacking; vegetative propagules: absent Apothecia: adnate, frequent, becoming contiguous, then 3-4 per areole, up to 0.3-0.6 mm in diam. disc: dark brown to black, persistently plane thalline margin: often lighter than thallus due to broken epinecral layer, 0.05-0.1 mm wide, entire and persistent; excipular ring: sometimes evident, confluent thalline exciple: 40-90 µm wide laterally, often confluent with areole margin; cortex: 5-10 µm wide; epinecral layer: often present, 5-10 µm wide; cortical cells: up to 4.5-7.5 µm wide, peripheral cells pigmented; algal cells: up to 8-14.5 µm in diam. proper exciple: sometimes pigmented light brown, 10-20 µm wide, expanding to 20-40 µm at periphery hymenium: 90-100 µm tall, paraphyses: 2-2.5 µm wide, conglutinate, with apices expanded up to 3.5-5 µm wide, lightly pigmented, immersed in dispersed pigment forming red-brown epihymenium; hypothecium: hyaline, 40-75 µm thick asci: clavate, 50-70 x 15-20 µm, 8-spored ascospores: brown, 1-septate, ellipsoid, type A development, Physconia-type, (16-)20-21(-25) x (8-)10-11(-13) µm, some spores narrowly swollen at septum, not more so in K, lumina angular at first (Physcia-like), lumina eventually filling cells, developing a pigmented endospore wall, spores waisted when overmature; torus: becoming pigmented; walls: lightly ornamented, best seen when lightly pigmented Pycnidia: superficial, pale brown, open, c. 0.1 mm in diam.; conidiophores: type I conidia: bacilliform, 4-5.5 x c. 1 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on calcareous rock and shale in coastal regions World distribution: endemic to western North America, with an oceanic distribution Sonoran distribution: at the southern limit of its distribution in Los Angeles County, California. Notes: The external morphology of R. pacifica is reminiscent of some forms of R. gennarii but the apothecia are larger and its thallus gray-brown rather than gray. The brown pigmentation of the cortex tends to be masked by an epinecral layer and is more evident when the thallus is moist. The spores are larger than those of R. gennarii and belong to the Physconia-rather than the Dirinaria-type. Rinodina pacifica may be related to R. innata, a species with a more limited distribution in coastal southern California and Baja California. The spores of the latter species are significantly smaller and belong to the Physcia-type.