Thallus: crustose, continuous to indistinctly rimose, thin, ±continuous; prothallus: absent surface: bright white, shiny, smooth, epruinose, phenocorticate, esorediate medulla: white, lacking calcium oxalate (H2SO4-) Apothecia: lecideine; (0.2-)0.4-0.5(-1) mm in diam., soon sessile margin: black, thin, ±persistent, sometimes excluded with age, rarely with a thalline veil when emerging from the thallus disc: black, epruinose, plane, becoming ±convex proper exciple: dispersa-type, inner excipular hyphae distinct, not reduced, pigmented, prosoplectenchymatous (textura oblita), extending from the deep reddish brown hypothecium (leptoclinoides-brown, textura intricata), outer excipular hyphae short-celled, cells angular, distinctly swollen (textura angularis) and ±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 to broadly ellipsoid, constricted, with obtuse ends, not curved, (16-)16.3-[18.1]-20(-21.5) x (8-)8-[8.6]-9.3(-10) µm (n=25); proper septum: narrow, not thickening during spore ontogeny (Buellia-type); ornamentation: rugulate (clearly visible at 400x magnification) Pycnidia: infrequent, 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, 13.5-20 x 0.5-1 µm (n=30) Spot tests: K+ bright yellow, P-, C- fluorescence: UV+ bright orange (in patches) iodine reaction: medulla non-amyloid Secondary metabolites: with unidentified xanthones; according to Marbach (2000) containing 6-O-methylarthothelin and lichexanthone, but not reacting C+ orange (the single specimen known from the Sonoran region was not analyzed with TLC or HPLC). Substrate and ecology: in the Sonoran Region currently known only from bark of Quercus World distribution: Marbach (2000) claims that the subtropical-tropical species is only known from Jamaica, even though Imshaug (1955) mentions in the protologue that he has seen material from the Gulf coast of the southeastern USA, and Sheard and May (1997) refer to several specimens collected by Harris in Florida, Georgia, and Louisiana Sonoran distribution: a single locality in Baja California Sur (Sierra La Laguna). Notes: Buellia leucomela can hardly be confused because of a combination of very distinct characters: rugulate ascospores, a smooth, continuous or barely rimose, brightly white thallus, which reacts conspicuously UV+ orange. The single Sonoran specimen fits the original description in Imshaug (1955), apart from the K+ yellow reaction. Its disjunct distribution is not all that uncommon. Buellia trachyspora is another species originally described from the West Indies that occurs in the subtropical-tropical areas of the Sonoran Region. Sheard and May (1997) placed B. leucomela into Amandinea based solely on its filiform conidia, but we do not agree with this placement. Because of the presence of xanthones (indicated by a distinct UV-fluorescence), the strongly rugulate ascospores and a subtropical-tropical distribution, B. leucomela appears not to be closely related to Buellia coniops, the type of Amandinea. Even if Amandinea is accepted, this species should therefore not be included.