Life habit: lichenized or lichenicolous Thallus: crustose, superficial, thin, continuous, subareolate to areolate surface: reddish or yellowish brown to dark olivaceous brown or white, smooth photobiont: primary one a chlorococcoid green alga, secondary one absent Ascomata: apothecial, partially immersed to sessile, black, lacking a thalline exciple disc: black, plane to convex, umbonate or gyrose exciple: persistent, black, brown or yellowish brown, often contorted to gyrose epihymenium: pale to dark brown or olivaceous hymenium: hyaline below, brown above, I+ blue; paraphyses: richly branched and anastomosed, septate, without swollen apices hypothecium: usually dark brown to black, sometimes yellowish brown, continuous with the exciple asci: cylindrical-clavate, Rimularia-type, 8-spored ascospores: ellipsoid to broadly ellipsoid or globose, non-septate, initially hyaline but becoming brown Conidiomata: pycnidial, immersed conidia: colorless, simple, bacilliform Secondary metabolites: usually none detected but orcinol and ß-orcinol depsides and ß-orcinol depsidones also present Geography: temperate and alpine habits throughout both hemispheres Substrate: usually on siliceous rocks or other lichens, sometimes on soil, mosses, wood or bark. Notes: The iodine reactions of the asci separate Rimularia from Porpidia. Although both have an I+ blue tubular reaction in the tholus, only Rimularia also reacts I+ blue along the flanks of the tholus.