Thallus: closely attached, at first thin, soon becoming rough and slightly uneven to almost bullate, later orbicular, in ±neat rosettes or spreading, c. 1 cm in diam.; prothallus: absent or white surface: green-gray, rugose cortex: often indistinct, occasionally up to 15 µm thick, hyaline, with a smooth upper surface: with interwoven, ±gelatinized hyphae algal layer: numerous cells 9-15 x 5-7 µm medulla: white, with loosely interwoven, thick-walled hyphae 3-5 µm thick, covered with tiny granules (soluble in K, insoluble in HCl) Apothecia: usually numerous, often crowded, sessile, somewhat constricted at the base, rounded, ±central, at first urceolate, finally 0.5-1(-1.5) mm in diam., 0.3-0.4 mm thick disc: dark brown to black, dull, concave to plane, sparsely pruinose margin: thick, concolorous with thallus, with a cellular cortex 25-35 µm thick exciple: often very indistinct, sometimes forming a pale yellow margin 10-15 µm wide, without distinct structure, occasionally in the upper part 30-50 µm thick and dark as the disc, over which it appears as a proper margin, laterally almost hyaline and little visible epihymenium: olive-brown, K+ purple or violet-brown, N+ yellow-brown, 15-20 µm thick hymenium: hyaline, somewhat opaque due to inspersion with numerous oil drops (visible especially in K), I- except for asci, (60-)70-85(-90) µm tall; paraphyses: 2-2.5 µm thick, becoming branched, with almost free, irregularly clavate, with brown pigmented tips 3-4 µm wide; hypothecium: hyaline to gray, opaque, 40-60 µm thick asci: cylindrical-clavate, Fuscidea-type, crowded to ±sparse, 60-80 x 15-20 µm, the wall 2.5-3.5 µm thick at top, I+ blue, darker in the apex, 75-100-spored ascospores: hyaline, simple, broadly ellipsoid, easily freed, 4-6 x 2.5-4 µm Pycnidia: immersed, ±globose, hyaline, c. 0.1 mm wide conidia: fusciform to oblong, c. 3 µm long Spot tests: medulla K-, C-, KC+ red, P- Secondary metabolites: alectorialic acid. Substrate and ecology: on bark of Cercocarpus in California World distribution: eastern, central and SW USA Sonoran distribution: southern California (Santa Cruz Island, Santa Monica Range and San Diego Co.). Notes: Potentially Maronea polyphaea might be confused with Tephromela atra or the subfusca group of Lecanora but its polysporous nature of the asci with their small spores quickly separate it from the latter possibilities. Without sectioning, one might also assume that it is a Rinodina species, but that genus has larger brown, 1-septate spores instead of hyaline, non-septate ones. The European and southern hemispheric M. constans (Nyl.) Hepp has sekikaic acid instead of alectorialic acid, and hence reacts KC- and has a thallus that can become warty-areolate.