Thallus: crustose, rimose to rimose-areolate, rarely becoming thickened and distinctly rimose-areolate to subsquamulose, thin, ±continuous; prothallus: absent surface: usually deep brown, rarely pale brown, dull or ±shiny, smooth, epruinose, phenocorticate, esorediate medulla: white, lacking calcium oxalate (H2SO4-) Apothecia: lecideine; (0.2-)0.3-0.5(-0.9) mm in diam., soon sessile margin: black, thin, ±persistent, excluded with age disc: black, epruinose, plane, sometimes ±convex proper exciple: narrow, poorly differentiated, aethalea-type, 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 with various amounts of a brown pigment (cf. elachista-brown, HNO3-) epihymenium: brown, pigmentation continuous with the outer exciple (HNO3-) hymenium: hyaline, not inspersed with oil droplets; paraphyses: simple to moderately branched, apically swollen, with a brown pigment cap (cf. elachistabrown) asci: clavate, Bacidia-type, 8-spored ascospores: soon brown, 1-septate, oblong to ellipsoid, usually not constricted, with obtuse ends, not curved, (9-)11.1-[12.5]-13.8 (-15) x (5-)6.2-[7.1]-8(-10) µm (n=91); proper septum: becoming soon but only briefly thickened during spore ontogeny (±Physconia-type), ornamentation: microrugulate (conspicuous in DIC at an early stage of the ontogeny) Pycnidia: common, globose, unilocular, at maturity lined with short barely branched conidiophores; ontogeny similar to the Roccella-type conidiogenous cells: terminal, not intercalary (conidiophore-type III) conidia: filiform, 6-33 x 0.5-1 µm (n=156) Spot tests: all negative (K-, P-, C-, KC-, CK-) fluorescence: UV-(dark) iodine reaction: medulla non-amyloid Secondary metabolites: none detected (J. A. Elix, HPLC). Substrate and ecology: epilithic, on siliceous mineral-poor rock (generally HCl-) World and Sonoran distribution: fairly common along the coast of southern California, Baja California and Baja California Sur, rarely inland in Sonora and southern Arizona. Notes: Buellia pullata is not synonymous with B. punctata, as suggested by Imshaug (1951). In the Sonoran region B. punctata occurs very rarely on rock, although Bungartz et al. (2004b) reported that they had not seen any saxicolous material of B. punctata. Indeed the only two saxicolous specimens identified as B. punctata since this publication are assigned here to B. punctata s.l. only with hesitation, because no conidia were found in the material. Conidia are usually the most reliable character to distinguish the two species. The majority of conidia in B. pullata are significantly longer than those in B. punctata s.str., although an enormous variation in length can usually be observed within one pycnidium. In contrast, B. punctata s.str. is characterized by relatively short, filiform conidia (mostly <18 µm). Spore characters of the two species are also different. Buellia pullata typically forms septal thickenings, but these are sometimes difficult to observe, because they develop only briefly during the ontogeny of the spore. Buellia punctata s. str. lacks septal thickenings. Thalli of B. pullata are typically thin, rimose, deep brown and fairly smooth, although not shiny. Even though they are often collected in dust-rich environments, they are typically not impregnated by mineral dust. Buellia punctata s. str. also forms rimose to rimose-areolate thalli that are typically not brown and usually have a slightly roughened surface, that frequently becomes impregnated with mineral dust. Apothecia of B. pullata usually remain ±flattened, but in B. punctata s. str., they are soon strongly convex.