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, crustose, endophloeodic, not disrupting the bark, c. 30 µm thick photobiont: Trentepohlia; cells 8-12 x 6-8 µm, in branched chains Ascomata: dispersed, broadly elongate to short-branched, 0.25-1 mm, in section 130-170 µm thick, disc: blackish brown, strongly convex; coarse, with crimson pruina, sometimes with admixture of white pruina; peripheric hyphal structures: parathecioid epihymenium: hyaline to pale brown, 20-30 µm thick, hydrophobic; hyphae: 2-3 µm wide, with brown walls, occasionally forming local zones at the periphery where short-celled hyphae (cells c. 4 µm in diam.) hymenium: ±hyaline, 60-70 µm tall, paraphysoids: branched and anastomosing; cells 5-7 x 0.5-1 µm; subhymenium: reddish brown, 50-70 µm thick; cells: ±round, with distinct gelatinous outer walls asci: dense, clavate, 50-60 x 13-17 µm, 8-spored, indistinctly stipitate, lateral endotunica thin ascospores: initially hyaline but soon becoming brown, 3-septate (not incised), septal formation proceeding downwards from the upper third (lowermost septum often more strongly pigmented), obovate, 15-19 x 5-7 µm, without an epispore, occasionally with anthraquinoid crystals at the septa with age Pycnidia: not observed Chemical reactions: ascomatal gels I+ blue, KI+ blue; epihymenial reddish pigments composed of a violet and a crimson fraction and K+ soluble, violet pigment K+ purplish red, crimson pigment K+ purplish violet; asci KI-. Substrate: on bark of various deciduous trees (Euphorbia, Aesculus) Sonoran distribution: Baja California (Cerro Kenton). Notes: Arthonia redingeri is clearly related to Arthonia cinnabarina, but differs in having smaller spores as well as different ascomatal shape and pigmentation pattern. It differs from A. speciosa by the lack of KI+ ring-structures in the tholus and by its ascomatal shape.