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, on apothecial discs of Rhizoplaca chrysoleuca Thallus: not apparent photobiont: absent Ascomata: immersed in the ascomata of the host, erumpent, ±round, up to 2 mm wide disc: black, often paler at the extending margins, slightly convex epihymenium: olive-brown, 15-20 µm thick; hyphal tips branched and enlarged, up to 3 µm thick hymenium: hyaline, 25-35 µm tall; subhymenium: hyaline, c. 20 µm thick asci: clavate, with distinct stipe, 28-33 x 14-17 µm, 8-spored ascospores: persistently hyaline, 1-septate, obovate, upper cell larger and longer, 10-14 x 4-7 µm, without an epispore Pycnidia: not found Chemical reactions: ascomatal gels I+ red, KI+ blue, with minute KI+ ring in tholus Substrate and ecology: see host World distribution: widespread throughout the range of its host Sonoran distribution: Arizona (Apache and Coconino Counties). Notes: Arthonia clemens is well characterized by its plane and extending ascomata on discs of Rhizoplaca and its hyaline subhymenium. It may also be present on Lecanora dispersoareolata, while other Lecanora species are infected by different Arthonia species (Grube and Matzer 1997). It is also found in New Mexico (Valencia Co.).