Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Thallus: crustose, rimose to rimose-areolate, thin, ±continuous; prothallus: absent surface: reddish brown ("leather colored"), dull, smooth, epruinose, phenocorticate, esorediate medulla: white, lacking calcium oxalate (H2SO4-) Apothecia: lecideine; (0.1-)0.2-0.4(-0.6) mm in diam., initially immersed, appearing aspicilioid, soon bursting through the thallus surface and becoming adnate to sessile margin: black (or color masked by grayish remains of necrotic thalline material, thalline veil), thin, usually persistent, rarely excluded with age disc: black, epruinose, plane, rarely becoming convex with age 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 usually strongly carbonized with various amounts of deeply aeruginose pigment (cf. elachista-brown and cinereorufa-green, HNO3+ violet) epihymenium: deeply aeruginose, pigmentation continuous with the outer exciple (HNO3+ strongly 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, oblong to ellipsoid, usually slightly constricted (with age), with obtuse ends, not curved, (10-)11.1-[12.2]-13.4 (-15) x (6-)5.9-[6.6]-7.3(-9) µm (n=68); proper septum: narrow, not thickening during spore ontogeny (Buelliatype); ornamentation: not visible in immature and premature spores, becoming microrugulate in mature spores (best seen 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, 4-7 x 1-1.5 µm (n=20) Spot tests: all negative (K-, P-, C-, KC-, CK-) fluorescence: UV- iodine reaction: medulla non-amyloid Secondary metabolites: none detected (J. A. Elix, HPLC). Substrate and ecology: epilithic, currently known only from siliceous volcanic coastal rock World and Sonoran distribution: Baja California (Gaudalupe Island and Pacific coast of the mainland). Notes: The thallus of B. tergua is very similar to that of B. pullata and B. christophii, even though these two species are generally darker brown. Apothecia of B. tergua, erupt from the thallus and young apothecia thus appear "aspicilioid". In B. pullata and B. christophii, apothecia emerge more gradually and young apothecia appear immersed but not aspicilioid. Neither of those species contain an aeruginose, HNO3+ violet pigment that causes a deep bluish green color of epihymenium and outer exciple in B. tergua. Conidia of B. tergua are bacilliform, but are filiform in B. pullata. For differences to B. ryanii see the description of that species.