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, usually thick and areolate but sometimes primarily endolithic, granulose or rimose; prothallus: often present, black areoles: corticated, gray, white or orange, sometimes sorediate medulla: white, I- or I+ blue photobiont: primary one a chlorococcoid green alga (Asterochloris), secondary one absent Ascomata: apothecial, scattered or clustered, partially immersed or sessile, up to 4 mm in diam., lacking a thalline exciple disc: black or dark brown, +pruinose margin: distinct, often prominent exciple: usually dark brown (rarely green) peripherally and gray, yellowish brown to dark brown internally, composed of radially oriented adglutinated hyphae hymenium: hyaline or pale green below, usually dark brown or greenish brown (rarely blue-green) above (N+ rose pink to purple), I+ blue; paraphyses: septate, branched and net-like and anastomosing, with +clavate apices; hypothecium: hyaline above but olivaceous brown to dark brown or brownish black below asci: clavate to subcylindrical, Porpidia-type (Vol. I), 8spored ascospores: hyaline, simple, ellipsoid to broadly ellipsoid, with a well developed perispore up to 7 µm thick Conidiomata: pycnidial, immersed in areoles, rare conidia: simple, hyaline, bacilliform Secondary products: ß-orcinol depsidones or orcinol depsides or none detected Geography: primarily boreal and montane regions of the Northern Hemisphere but extending to Australasia and South America Substrate: usually on acidic but occasionally on calcareous rocks, rarely on wood and made-made substrates. Notes: Superficially Porpidia resembles Lecidea s.str., but has a distinctive ascus type that places it closer to Amygdalaria, Clauzadea and Farnoldia. Zahlbruckner (1930) placed species of what is now recognized as Porpidia into the genus Huilia. Occasionally P. crustulata and P. macrocarpa in our region become orange or rusty red due to iron accumulation from their substrate.