Life habit: lichenized Thallus: squamulose, sometimes apparently small foliose or crustose, thallus margin often effigurate, stellate to flabellate, sometimes a bluish prothallus present, not gelatinous when wet upper surface: dark olive, brownish or blackish, sometimes grayish pruinose, smooth, uneven, granulose, nodulose or covered by isidia anatomy: indistinctly corticate and stratified photobionts: a filamentous cyanobacterium, Scytonema or species of Rivulariaceae, secondary photobiont absent lower surface: usually blackish due to the presence of a hypothallus composed of interwoven bluish-black hyphae, rarely pale and hypothallus lacking Ascomata: apothecial, laminal on thallus, orbicular, half-immersed to sessile or stipitate; margin: distinct to prominent, without thalloid rim or rarely with thalloid margin; exciple: thin or thick, of radiating hyphae; epithecium: dark violaceous to brownish, hymenium: often violaceous; hypothecium: hyaline to brownish asci: lecanoral, apex thickened, with amyloid tube, (4-) 8-spored ascospores: simple when immature, septate when mature, ellipsoid or elongate-fusiform to broadly ellipsoid; 7-53 x 3.5-9 µm; wall: thin, hyaline Conidiomata: pycnidial, laminal, immersed, dark colored conidia: dumbbell-shaped, ellipsoid or bacilliform, c. 2.5-5 (-8) x 1 µm Secondary metabolites: none detected Geography: cosmopolitan, usually in wet microhabitats, sometimes in exposed situations Substrate: calcareous or siliceous rock, rarely bark or soil. Notes: The foliose genera Koerberia and Vestergrenopsis are superficially similar, but they, of course have a lower surface that is pale. In addition, they have a pale, striate upper surface and lecanorine apothecia. Parmeliella is similar in the presence of a blackish hypothallus but has Nostoc as photobiont. Well developed thallus margins are essential for proper species determinations. Placynthium flabellosum is known from northern California and may eventually be found in the Sonoran region.