Thallus: crustose, usually growing in distinct circular patches, rimose to rimose-areolate, subeffigurate, several thalli often confluent, thin to thick (thin thalli appearing continuous to infrequently cracked; thick thalli rimose-areolate but areoles poorly delimited); prothallus: delimiting the thallus margin, distinctly blackened to pale gray, rarely white and indistinct surface: usually white, rarely pale gray, dull, chalky, heavily pruinose, phenocorticate, with a thick epinecral layer of dead cells and calcium oxalate crystals, esorediate medulla: chalky, usually white, filled with an abundance of calcium oxalate (H2SO4+ needle shaped crystals) Apothecia: lecideine, but rarely pseudolecanorine, i.e., surrounded with outer ring of poorly differentiated thalline material (thalline collar); (0.2-)0.3-0.4(-0.7) mm in diam., immersed, becoming adnate to sessile margin: black, thin, rarely persistent, usually excluded with age, rarely surrounded by a thalline collar disc: black, epruinose or whitish pruinose, plane, soon becoming convex proper exciple: narrow, poorly differentiated, aethaleatype, inner excipular hyphae narrow, hyaline, prosoplectenchymatous (textura oblita), often reduced, similar in structure and orientation to the paraphyses, transient with the deep reddish brown hypothecium (leptoclinoides-brown, textura intricata), outer excipular hyphae parallel, moderately swollen (textura oblita) and strongly carbonized, olive-brown from a mixture of brown and aeruginose pigments (cf. elachista-brown and cinereorufa-green, HNO3+ violet) epihymenium: brown, pigmentation continuous with the outer exciple (HNO3+ violet) hymenium: hyaline, not inspersed with oil droplets; paraphyses: simple to moderately branched, apically swollen, with a brown pigment cap (cf. elachista-brown) asci: clavate, Bacidia-type, 8-spored ascospores: soon brown, 1-septate, narrowly oblong to ellipsoid, not constricted, with obtuse ends, not curved, (8-)10.4-[11.6]-12.8(-15) x (4-)5.1-[5.8]-6.5(-8) µm (n=615); proper septum: narrow, not thickening during spore ontogeny (Buellia-type); ornamentation: not visible in DIC Pycnidia: rare, globose, unilocular; ontogeny similar to the Umbilicaria-type conidiogenous cells: mostly terminal, rarely also intercalary (cf. conidiophore-type V) conidia: bacilliform, 2.5- 4 x 1-1.5 µm (n=30) Spot tests: thallus typically K+ yellow to red (crystals), P+ yellow, C-, KC-, CK- (K and P reactions usually well pronounced, rarely absent) fluorescence: UV- iodine reaction: medulla non-amyloid Secondary metabolites: norstictic acid with connorstictic acid, rarely secondary metabolites absent. Substrate and ecology: epilithic, on rock substrates with traces of calcium carbonate (limestones, carbonate-rich sandstones, HCl+), often in nutrient enriched sites, often growing associated with B. venusta, from coastal areas at low elevations World distribution: southwestern North America and the Mediterranean regions of southern Europe and North Africa Sonoran distribution: along the coast of southern California, Baja California, and Baja California Sur. Notes: Bungartz and Nash (2004b) placed B. maritima into synonymy with B. subalbula. More recent studies demonstrated that the two taxa do not represent the same species, but are separate, distinct species that belong to a diverse species group characterized by one septate spores and large amounts of calcium oxalate in the thallus (Bungartz and Grube 2005). Scheidegger (1993) suggested that B. maritima was a synonym of B. stellulata, but the two species are distinctly different, as specimens of B. maritima are rimose to rimose-areolate, densely pruinose and contain large amounts of calcium oxalates. Almost all specimens examined contain norstictic acid. Buellia stellulata has a distinctly areolate thallus, and its individual areoles are typically surrounded by a conspicuous black hypothallus. Some specimens of B. maritima are delimited by a black prothallus, which, however, never extends to form a hypothallus. Unlike B. maritima, B. stellulata does not contain significant amounts of calcium oxalates, nor does it produce norstictic acid. Both species are distributed along the coast, but B. maritima is restricted to substrates that contain calcium carbonate, whereas B. stellulata prefers purely siliceous rocks. Buellia maritima very closely resembles B. venusta and, in the Sonoran Region, often grows with that species. The two species can easily be distinguished by their spores: one-septate spores in B. maritima, pluriseptate spores in B. venusta.