Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.
Life habit: lichenized Thallus: crustose, squamulose or placodioid, continuous, granulose, rimose or areolate surface: green, gray, yellowish to olivaceous brown or whitish red, sometimes sorediate photobiont: primary one a chlorococcoid green alga (Chlorella), secondary one absent Ascomata: apothecial, orbicular, partially immersed to sessile, yellow-brown to reddish black margin: biatorine, distinct and prominent exciple: brown, yellowish brown or hyaline hymenium: hyaline below, hyaline to yellowish brown above; paraphyses: distinctly branched and anastomosing; hypothecium: brown, yellowish brown or hyaline asci: clavate to cylindrical, unitunicate, thin-walled, I-; apical dome I-or weakly I+ blue; 8-spored ascospores: hyaline or faint pink, simple, ellipsoid, 14-32 x 6-14 µm, smooth, without a distinct perispore Conidiomata: pycnidial, immersed, with an exobasidial fulcrum conidia: oblong-cylindrical to filiform Geography: cosmopolitan Substrate: soil, mosses, wood, bark or siliceous rocks. Notes: Trapeliopsis is very similar (see under that genus for differences). Placynthiella has a exciple of brown-walled pseudoparenchymatous cells and paraphyses with irregularly capitate apices, each crowned with a dark brown apical cap.