Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Life habit: lichenicolous Galls: beneath ascomata, up to 150 µm thick, made entirely of brown prosoplectenchymatic hyphae, hyphae 4-5 µm wide photobiont: absent Ascomata: ±round, 0.3-0.9(1.3) mm wide disc: black, ±convex, epruinose epihymenium: ±brown, 0-5 µm thick, hyphae poorly developed, hymenium: hyaline to light brown, 40-50 µm tall; paraphysoids: simple to poorly branched, tips up to 3 µm wide; subhymenium: hyaline, 30-40 µm thick, not sharply delimited to subtending gall-structures asci: clavate, 30-45 x 11-16 µm, 8-spored ascospores: narrowly obovoid, not or slightly constricted at the septum, 10-12 x 3-4 µm, with a distinct epispore Pycnidia: not observed Chemical reactions: ascomatal gels I+ red, KI+ blue; without a KI+ tholus structure. Substrate and ecology: parasitic on Heterodermia species World distribution: Mexico and Colombia Sonoran distribution: western Chihuahua. Notes: Arthonia tremelloides is fairly well charactized by the formation of gall structures. The galls of A. tremelloides are produced by hyphae of the parasite. Superficially, the species resembles Plectocarpon, but ascus characters clearly indicate its relationships with Arthonia. Only one other species of Arthonia forms similar galls: A. plectocarpoides on Pseudocyphellaria, which is known from Chile.