Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Thallus: crustose, thin, usually growing in distinct circular patches, subeffigurate, several thalli often confluent, epilithic; continuous to rimose with fine fissures; prothallus distinct, delimiting the thallus as a black outline surface: usually white, rarely gray, chalky, dull, heavily pruinose, phenocorticate, esorediate medulla: white, filled with an abundance of calcium oxalate (H2SO4+ needle shaped crystals) Apothecia: lecideine; (0.3-)0.5-0.8(-1.1) mm in diam., remaining immersed to indistinctly adnate margin: thick, persistent, not excluded with age, black, usually covered with a dense, fine, white pruina disc: black, usually with dense, fine, white pruina, plane, not becoming convex with age proper exciple: similar to the aethaleatype, inner exciple almost entirely reduced, hyphae narrow, hyaline, prosoplectenchymatous (textura oblita), similar in structure and orientation to the paraphyses, transient with the deep reddish brown hypothecium (leptoclinoidesbrown, textura intricata), outer exciple expanded, globular cells strongly swollen (textura oblita) and moderately carbonized with 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. elachista-brown) asci: clavate, Bacidia-type, 8-spored ascospores: soon brown, 1-septate (rarely with additional septa forming at both ends), oblong to ellipsoid, usually not constricted, with obtuse ends, not curved, (12-) 15-[16.8]-18.5(-20) x (6-)6.5-[7.3]-8.1(-9) µm (n=60); proper septum: narrow, not thickening during spore ontogeny, (Buellia-type); ornamentation: rugulate (visible without DIC) Pycnidia: rare, urceolate to globose, unilocular, at maturity almost entirely occupied by densely branched conidiophores; ontogeny similar to the Umbilicaria-type conidiogenous cells: mostly terminal, rarely also intercalary (cf. conidiophore-type V) conidia: bacilliform, 4-6.5 x 1-1.5 µm (n=20) Spot tests: thallus typically K+ faint yellow (yellow solution, but no orange crystals observed in the microscope), P+ faint yellow, C-, KC-, CK- (reactions usually inconspicuous) fluorescence: UV+ pale white iodine reaction: medulla amyloid Secondary metabolites: norstictic, connorstictic, stictic and hypostictic acid, and an unknown xanthone (RF 7, not visible in natural light, UV+ orange). Substrate and ecology: on limestone (strongly HCl+) World distribution: poorly known, at least in Mexico Sonoran distribution: very rare, currently known from a single location in Sinaloa. Notes: Buellia argillicola is easily recognized because of its thick, almost continuous rimose thallus rich in calcium oxalates, its instantaneous deep blue medullary iodine reaction, and its immersed strongly pruinose apothecia with thick lecideine margins. Very little is currently known about the distribution of this species that was originally described from central Mexico.