parathecium: up to 60 µm thick, often forming parathecial crown Ecology and substrate: on sandstone and granite lateral cortices: paraplectenchymatous, 20-45 µm thick; cells: irregular, 3-4 µm wide; eucortex with a diffuse yellow layer above 10-25 µm thick, hyaline layer below 10-23 µm thick lower surface: lacking or ecorticate exciple: usually distinct, thick beneath subhymenium, broadening sometimes to 50-80 µm above disc, forming a inner ring around the disc Thallus: areolate, small, determinate, orbicular or not, less than 2 cm. across areoles: becoming squamulose, 2-4 mm. across, sometimes lobulate; margin: indistinct to distinctly effigurate; lobes: poorly developed, 0.5-1(-2) mm long, up to 1 mm thick upper surface: yellow-orange, smooth, becoming convex, epruinose cortex: 30-60 µm thick, with an outer, 20-40 µm thick yellowish brown layer and an inner, colorless layer algal layer: 50-200 µm thick; algae up to 10 µm diam. medulla: white, prosoplectenchymatous, intricate Apothecia: 1-3 mm wide, numerous on thallus disc: pale yellow, only slightly brown, scarcely darker than thallus with thalline margin, plane becoming convex to almost globose, sometimes corrugated, biatorine, margin completely excluded true exciple: colorless, 50-80 µm thick epihymenium: brownish yellow, 15-20 µm thick hymenium: hyaline, usually 50-70 µm tall; paraphyses: simple or poorly branched, 2 µm or less broad at base, not or scarcely thickened at apex asci: clavate, 70-80 x 15-20 µm, 100-200-spored ascospores: hyaline, simple, ellipsoid, 3.5-4.5 x 1.5-2 µm Pycnidia: immersed conidia: ellipsoid, 3-3.8 x 1.5-1.8 µm Spot tests: thallus UV+ orange, K-, C-, KC-, P- Secondary metabolites: containing rhizocarpic, acaranoic, acarenoic acids (race 1), or in N. America also rhizocarpic and roccellic acids (race 2). Substrate and ecology: on rock, especially under overhangs on cliffs World distribution: Antarctica, Europe, North and South America Sonoran distribution: southern California (Santa Cruz Island) . Notes: Pleopsidium chlorophanum differs from P. flavum in having a smooth, smaller squamulose thallus and larger apothecia. For a long time, all effigurate specimens from North America have been called Acarospora chlorophana going back to Tuckerman in the 1800's. Pleopsidium chlorophanum is a rare, alpine species in Europe. In contrast, Pleopsidium flavum is a Mediterranean species, which was recognized after P. chlorophanum, and it has a broader ecological amplitude. It is assumed P. chlorophanum occurs in North America at high elevations, but so far we have seen only one specimen from North American, a collection by Charis Bratt (#3436, SBBG!) from a rock in grassy filed on Santa Cruz Island in southern California.