Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.

Life habit: lichenized or saprobic Thallus: crustose, mostly immersed in substrate, or byssoid with black subiculum, or absent photobiont: a trentepohlioid alga or absent Ascomata: perithecial, circular to ellipsoid in surface view involucrellum: clypeate, dark brown, composed of compacted hyphae and bark cells; true ascomatal wall: black, not continuous below the hamathecium exciple: thin, usually colorless, surrounding center hamathecium: usually branched, anastomosing, ± moniliform pseudoparaphyses, non-amyloid, or disappearing and than sometimes amyloid; periphysoids: also present asci: bitunicate, pyriform to clavate, with tholus, non-amyloid, 8-spored ascospores: usually hyaline but sometimes brownish with age, pyriform to clavate, 1-3-septate with eusepta, 4-16 x 12-50 µm; walls: sometimes ornamented with tiny warts Conidiomata: pycnidial, blackish conidia: simple to 1-3-septate, oblong, ovoid, bacilliform or thread-like Secondary metabolites: absent Geography: cosmopolitan Substrate: mostly on bark, but also on non-calcareous rock. Notes: Sonoran species of this genus have recently been classified in four different genera in three different families (Harris 1995a), but the differences between species of Arthopyrenia are not very discrete and do not warrent a separation at the generic (let alone familial) level. The genus is, in this wide concept, characterized by the branched, but not anastomosing pseudoparaphyses, which may disappear in later stages, and the usually somewhat sole-shaped ascospores, which always have a broader and shorter upper cell and a longer but more slender lower cell.