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DescriptionLife 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.