Diagnosis:—Sicut Buellia saxicola sed thallo sulphureo, apotheciis minutis et hypothecio hyalino (see also Buellia sulphurica at EOL)
Type:—ECUADOR. Galápagos: Isabela Island, Volcán Alcedo, upper NNW-exposed slope inside the crater, 0°27’S, 91°7’W, 1055 m, open vegetation with Adianthus concinnum and scattered shrubs of Tournefortia rufosericea among basalt blocks in the vicinity of the sulfur vents, on basalt, March 2006, Aptroot 64881(holotype CDS-31458, isotype ABL).
Thallus crustose, thin, of dispersed groups of areoles, marginal ones ± subsquamulose, epilithic; prothallus absent; thallus surface matt, bright neon yellow, finely whitish pruinose, phenocorticate; thallus densely filled with fine crystals (ca. 5 μm in diameter, dissolving in 10% KOH), and few large mineral crystals (irregular in diameter, ca 30–50 μm, not dissolving). Apothecia lecideine, initially inconspicuously lecanorine; (0.10–)0.15–0.25(–0.30) mm in diameter; soon adnate to sessile; proper margin black, soon excluded, when emerging typically covered by coarse, thick thalline fragments; disc black, epruinose, initially plane, but soon strongly convex; thalline exciple, if present, poorly developed and reduced to very few adglutinated hyaline hyphae densely packed with photobiont cells, ± merging with the surrounding thallus; proper exciple similar to the aethalea-type sensu Scheidegger (1993), but strongly reduced to few, parallel hyphae, almost indistinct from the paraphyses, apically moderately swollen (textura oblita) and reddish brown (cf. elachista-brown, HNO3–), pigmentation continuous with the epihymenium; excipular hyphae downward soon losing pigmentation and not clearly differentiated from either hymenium or hypothecium, hymenium hyaline, not inspersed with oil droplets; paraphyses simple to moderately branched, apically swollen, with a brown pigment cap (cf. elachista-brown). Asci 8-spored, clavate, Bacidia-type. Ascospores oblong, not constricted with age, with obtuse ends, not curved, (9.8–)10.7–[12.1]–12.7(–13.7) × (5.9–)6.0–[6.6]–6.7(–6.8) μm (n = 25), 1-septate, proper septum briefly thickened during spore ontogeny (Physconia-type); ornamentation absent (not visible in DIC). Pycnidia not found. Secondary chemistry: rhizocarpic acid; thallus P−, K−, C−, KC−, CK−; thallus surface and medulla not amyloid (always test with concentrated Lugol's iodine or in the compound microscope; thallus reactions can be very weak!), the hymenium reacts amyloid in Lugol's.
Distribution:—Known only from Galápagos, on Isabela Island (Volcán Alcedo: north-northwest exposed inner caldera rim; Volcán Chico: along northern outer slope of Sierra Negra); on basalt (HCl–), close to volcanic sulphur vents. Etymology:—The epithet refers both to the thallus colour and the close approximation to sulphur vents.
Additional specimens examined (paratypes):—ECUADOR. Galápagos: Isabela Island, Volcán Alcedo, upper NNW-exposed slope inside the crater, Aptroot 64815, 64798, 64800, 64797 (CDS). Volcán Chico, on the N outer slope of the caldera of Sierra Negra, Bungartz 8732 (CDS-44070).
Notes:—Despite its minute size, it is a very conspicuous species, unlikely to be overlooked in the field because of its bright neon colour. Found only near sulphur vents. Both the conspicuous colour and its unusual habitat suggest that the species could be truly endemic to the archipelago. The species is very unusual not only because of its habitat and presumed high tolerance to sulphur. It contains rhizocarpic acid, a substance very rarely encountered in Buellia and known only from few species of uncertain taxonomic placement, e.g. Buellia centralis H.Magn. (Lamb 1968, Obermayer et al. 2004). The apothecia have a hyaline hypothecium that is typically regarded as diagnostic for Rinodina rather than Buellia; as very few species of Buellia are known to possess a weakly or completely unpigmented hypothecium. The ascospores show Physconia-type ontogeny, i.e., they initially have a thickened septum, becoming reduced with age. This spore type is seen both in Buellia and Rinodina. The apothecia are unusually small, have a strongly reduced proper exciple, and, when emerging from the thallus, large chunks of thalline material initially remain attached. Nevertheless they never develop a distinctly lecanorine margin. The main reason why the species is described here in Buellias.lat. is the typical Bacidia-type ascus, which in Lugol has the characteristic deep blue flanks merging at the tip and a thin, unstained inner tholus axis.
from: Lumbsch, H.T., Ahti, T., Altermann, S., Amo De Paz, G., Aptroot, A., Arup, U., Bárcenas Peña, A., Bawingan, P.A., Benatti, M.N., Betancourt, L., Björk, C.R., Boonpragob, K., Brand, M., Bungartz, F., Cáceres, M.E.S., Candan, M., Chaves, J.L., Clerc, P., Common, R., Coppins, B.J., Crespo, A., Dal Forno, M., Divakar, P.K., Duya, M.V., Elix, J.A., Elvebakk, A.V., Fankhauser, J., Farkas, E., Ferraro, I.L., Fischer, E., Galloway, D.J., Gaya, E., Giralt, M., Goward, T., Grube, M., Hafellner, J., Hernández M., J.E., De Los Ángeles Herrera Campos, M., Kalb, K., Kärnefelt, I., Kantvilas, G., Killmann, D., Kirika, P., Knudsen, K., Komposch, H., Kondratyuk, S., Lawrey, J.D., Mangold, A., Marcelli, M.P., Mccune, B., Messuti, M.I., Michlig, A., Miranda Gonzáles, R., Moncada, B., Naikatini, A., Nelsen, M.P., Øvstedal, D.O., Palice, Z., Papong, K., Parnmen, S., Pérez-Ortega, S., Printzen, C., Rico, V.J., Robayo, J., Rosabal, D., Ruprecht, U., Salazar Allen, N., Sancho, L., Santos De Jesus, L., Santos Vieira, T., Schultz, M., Seaward, M.D.R., Sérusiaux, E., Schmitt, I., Sipman, H.J.M., Sohrabi, M., Søchting, U., Søgaard, M.Z., Sparrius, L.B., Spielmann, A., Spribille, T., Sutjaritturakan, J., Thammathaworn, A., Thor, G., Thüs, H., Timdal, E., Truong, C., Türk, R., Umaña Tenorio, L., Upreti, D.K., Van Den Boom, P., Vivas Rebuelta, M., Wedin, M., Will-Wolf, S., Wirth, V., Wirtz, N., Yahr, R., Yeshitela, K., Ziemmeck, F. & Lücking, R. (2011): One hundred new species of lichenized fungi: a signature of undiscovered global diversity. Phytotaxa 18: 1-127.