Thallus: areolate, effigurate or subsquamulose, marginally crenate to lobed, often lumpy-squamulose, smooth or minutely rugose areoles: +convex, often +overlapping; marginal squamules 0.2-0.4 mm wide and 0.04-0.15(0.12) mm thick, contorted, sometimes in irregular, knotted clusters surface: mostly beige, gray or brownish white Apothecia: round, scattered, 0.2-0.8(-2) mm in diam. disc: rose-pink to red-brown or brown-black, +roughened, often with a thin margin: white, smooth to crenate, pseudothalline caused by its eruption through the thallus, part of which may remain adhering, +forming a halo-like rim, at least when young hymenium: hyaline below, hyaline to yellowish brown above, 90-140 µm high; hypothecium: colorless ascospores: simple, 14-25 x 7-13 µm Pycnidia: immersed conidia: filiform Spot tests: thallus K-, C+ pale red, KC+ pale red, P- Secondary metabolites: thallus with gyrophoric acid chemosyndrome. Substrate and ecology: on +siliceous rocks (also on brick), often on pebbles near the ground, rarely on worked timber, and occasionally on peaty turf amongst rocks, especially those on the coast; in rather humid and shaded situations World distribution: cosmopolitan Sonoran distribution: eastern Arizona, southern California, and Baja California. Notes: Trapelia involuta differs from T. coarctata mainly in its better developed and more brownish or grayish thallus.