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DescriptionLife habit: lichenized; Thallus: ±crustose or finely squamulose, when crustose areolate, rimose, or entirely without cracks, rarely discontinuous, discrete to contiguous areoles; prothallus absent; surface: smooth, wrinkled, or warted, often partly or entirely dissolving into soredia; cortex: varying from absent to present, when present consisting of a phenocortex and an epinectral layer, both lacking crystals; medulla: very thin, often indiscernable; photobiont: primary one chlorococcoid green alga, secondary one absent; Ascomata: apothecial, biatorine, up to c. 1 mm wide; disc: usually pink, gray-, red-, or purple-brown, or black, epruinose, containing various combinations of a green to blue-green (K-, N+ purple), brown (K+ purplish, N+ orange), pale yellow to orange (K+ intensifying, N+ intensifying), dirty brown (K+ greenish, N-), and a bronze-yellow (K-, N-) pigment; exciple: annular, at least in lower (older) part, paraplechtenchymatic, composed of radiating, ±branched and ±anastomosed hyphae with thin, gelatinized, conglutinated walls, and thin to very wide, cylindrical to globose lumina, which are wider in the lower (older) than in the upper (younger) part of the exciple; terminal cells of the excipular hyphae: not or only very slightly enlarged; crystals: rarely present, minute, along edge of exciple; epithecium: distinct or indistinct, containing pigment and rarely crystals; hymenium: hyaline, 25-80 µm tall; paraphyses: straight, 1-2 µm wide in mid-hymenium, conglutinated or not, unbranched or ±branched in upper part, sometimes very sparingly anastomosed; apical cells: often swollen, never with a distinct hood of pigment; hypothecium: colorless to brown, without crystals and oil droplets, not chondroid; asci: clavate, surrounded by a gelatinous, amyloid sheet, with a well-developed, amyloid tholus containing a ±conical ocular chamber (sometimes poorly developed), a ±conical, dome-shaped, or cylindrical axial body, and sometimes a deeper amyloid zone around the axial body (Bacidia-, Biatora-, or Lecanora-type or derivatives of these), 8-spored; ascospores: hyaline, transversely 3- to many-septate, almost bacilliform to clavate to acicular, straight, curved or sigmoid, without halo or perispore; Conidiomata: pycnidial, campylidial, or 'brush-like conidiomata' sensu Sérusiaux (1995), when pycnidial ±immersed, colorless or upper part of wall containing same pigments as apothecia, unilocular, with short, sparingly branched conidiophores and ampulliform conidiogenous cells; conidia: acrogenous, (1) filiform, straight to curved, non-septate or up to 11-septate, conglutinated or not, or (2) bacilliform, non-septate or with few septa, or (3) acicular, non-septate; Secondary metabolites: none detected; Geography: arctic to tropical regions of the world; Substrate: mostly bark or vascular plant leaves, also on wood, rock, decaying bryophytes, detritus, soil, and various anthropogenic substrates (e.g., metal, leather, plastic, bricks, tiles).; Notes: There has been debate concerning the use of the name Bacidina, as this name is antedated by both Woessia and Lichingoldia. A proposal to conserve Bacidina against the two earlier names (Ekman 1996b) has been recommended (Gams 2001). In addition, it has been recently suggested that Lopacidia Kalb (Kalb 1984) is a further earlier name for Bacidina (Kalb, Lücking & Sérusiaux 2000). However, the type material of Patellaria multilocularis Möll. Arg. in G, on which Lopacidia is based, is a member of Bacidia in the strictest sense that should be named Bacidia multilocularis (Möll. Arg.) Zahlbr. Consequently, Lopacidia is a younger synonym of Bacidia. The misinterpretation has possibly been brought about by confusing the paraplechtenchymatic proper exciple in species of Bacidina with the rather wide zone of enlarged cell lumina, formed by the terminal cells of the excipular hyphae, along the rim of the proper exciple in B. multilocularis. A similar zone of enlarged cell lumina is present also in some other members of Bacidia s. s., e. g., B. campalea (Tuck.) S. Ekman & Kalb, B. russeola (Kremp.) Zahlbr., and B. suffusa (Fr.) A. Schneid. (Ekman 1996a). Bacidina is classified here in the Ramalinaceae; see note under Bacidia. The generic description above refers to Bacidina s. s., which does not include B. ramea (see under that species). Pigment deficient morphs of Bacidia subincompta with more or less pinkish apothecia are often mistaken for species of Bacidina with little or no pigment in the apothecia. Such morphs of B. subincompta can be separated from Bacidina on account of the prosoplechtenchymatic proper exciple, and wider, often fusiform ascospores.