Thallus: crustose, growing as discontinuous irregular crust, if well developed becoming irregularly granular in parts, otherwise entirely hidden in the substrate, thin to very thin or almost absent, partially hidden in the substrate; prothallus: absent surface: grayish white to olive brown, dull, epruinose, phenocorticate or lacking a distinct cortex, esorediate medulla: white, lacking calcium oxalate (H2SO4-) Apothecia: lecideine (or ±biatorine); (0.1-)0.2-0.3(-0.4) mm in diam., soon sessile margin: very dark reddish brown to black, thin, rarely persistent, soon excluded disc: very dark reddish brown to black, epruinose, plane, very soon becoming 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 to distinctly swollen (textura oblita) weakly to 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. elachista-brown) asci: clavate, Bacidia-type, 8-spored ascospores: soon brown, 1-septate, ellipsoid, not constricted, with obtuse ends, not curved, (6.5-)7-[8.4]-9.8(-11) x (3-)3.4-[3.9]-4.4(-5) µm (n=26); proper septum: narrow, not thickening during spore ontogeny (Buellia-type); ornamentation: not visible in DIC Pycnidia: rare, globose, unilocular, at maturity almost entirely occupied by unbranched, elongated conidiophores; ontogeny similar to the Umbilicaria-type conidiogenous cells: always terminal, (conidiophore-type II) conidia: bacilliform, very short, some almost globose, 1.5-3 x 0.5-1 µm (n=50) Spot tests: K- or K+ yellow, P-, C- fluorescence: UV- (pale) iodine reaction: medulla non-amyloid Secondary metabolites: atranorin, or no substances detected (J. A. Elix, HPLC). Substrate and ecology: on bark or rarely wood World distribution: very widely distributed, cosmopolitan species easily overlooked due to its inconspicuous thallus and very small apothecia Sonoran distribution: a single locality in Chihuahua. Notes: Buellia schaereri is easily recognized by its very small ascospores. Buellia schaereri was previously assumed to be a circumboreal, Northern Hemisphere species. With the inclusion of B. endachroa, the distribution area has been extended to the subtropics and tropics. Marbach (2000) included B. endachroa within Amandinea, even though he did not find conidia in the material he studied. However, the type of B. endachroa in S has pycnidia with very small, bacilliform conidia on single-celled, elongated conidiophores. These are identical with conidia and conidiophores studied in B. schaereri. Malme (1927) originally used the spelling endachroa, both in the protologue and on the type labels. This spelling should therefore not be changed to endochroa, as it was not an orthographical error.