Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Life form: lichenized Thallus: white-gray, with integrated bark fragments, 60-80 µm thick photobiont: trentepohlioid; cells: c. 8 x c. 6 µm Ascomata: scattered, lirellate, broadly erumpent, large ascomata sometimes fissured or cracked, up to 2 mm in diam., in section 100-150 µm thick, at the same level with thallus or emerged, all layers of the ascomata interspersed with dark yellow orange crystals; crystals: large, irregularly shaped, often grain-like to slightly elongated disc: appearing brown to black, ±plane surface; peripheric hyphal structures: indistinct epihymenium: hyphae hyaline, 50-60 µm thick, hyphal structures similar to those of the layers below hymenium: hyphae hyaline, c. 100 µm tall; paraphysoids: branched and anastomosing, not concentrated around asci; cells: 3-4 x 0.5-1 µm, sinuous; subhymenium: hyphae hyaline, c. 30 µm thick asci: subglobose, 100-110 x 55-65 µm, 8-spored, stipitate, lateral endotunica thickened ascospores: hyaline, brownish when aborted, strongly muriform, isolocular, with 7-9 transverse septa and (1)2-4 longitudinal septa in each transverse segment, oblong ovoid to ellipsoid, 48-60 x 15-22 µm, with c. 0.7 µm thick walls Pycnidia: not observed Chemical reactions: ascomatal gels I+ blue becoming red with blue patches, KI+ blue around the asci and yellow blue in other parts of the ascomata; in the epihymenium K+ orange crystals completely dissolving and indistinctly pale violet; asci with KI+ broad, blue ring structure; endotunica walls of released and old asci KI+ blue. Substrate and ecology: so far known on smooth bark of trees World distribution: Greater Antilles (Cuba), Central America (Costa Rica), and North America (Mexico) Sonoran distribution: Sinaloa. Notes: Arthonia mirabilis is characterized by its remarkable dark yellow pigments in the ascomata. The ascomata are black and epruinose in external appearance. Its dark yellow pigment is distinct in cross sections. It turns temporarily purple in K and completely dissolves subsequently. Beside the yellow crystals found in all ascomatal layers, no other pigments are recognized. The systematic position of this species is unclear.