Thallus: areolate, verrucuate, or squamulose, dispersed or more usually contiguous, indeterminate, up to 10 cm wide or more across upper surface: yellow, glossy, plane, smooth, but becoming convex and pleated, epruinose or rarely pruinose upper cortex: 35-130 µm thick; syncortex: thin, indistinct up to 15 µm thick; eucortex: upper half: yellow, obscure, paraplectenchymatous to subprosoplectenchymatous, with cells various in size, round to angular, and obscure; lower layer hyaline, prosoplectenchymatous, intricate to anticlinal, to subparaplectenchymatous, various in shape, size and orientation, the whole cortex formed from differentiation of hyphal bundles penetrating through algal layer lower surface: narrow, yellow to white or brown algal layer: 100-300 µm, with cells up to 18 µm in diam., even but thin in the beginning, eventually interrupted by hyphal bundles and becoming uneven and jagged medulla: prosoplectenchymatous, continuous with attaching hyphae, with no clear demarcation, anticlinal to intricate, penetrating the substrate, with both thin hyphae up to 2 µm wide as well as occasional thick, hyaline rhizines to 4-5 µm wide attachment: broad, eventually developing a stipe Apothecia: usually one per areole or squamule, sometimes two or three; undivided areoles or squamules can have multiple units with multiple apothecia, even forming pin-wheel-like conglomerations of reduced apothecia disc: usually dark reddish brown, 0.4-0.7(-1.2) µm across, plane, rough, epruinose, often filling areole parathecium: 10-30 µm wide, not expanding around disc epihymenium: reddish brown to yellow, 10-15 µm thick, strongly conglutinate hymenium: 90-140 µm, pale yellow in upper third, hyaline below; paraphyses: c. 2 µm wide below, with apices barely expanded, many with dark caps subhymenium: hyaline to pale yellow, 40-80 µm thick; hypothecium: 10-30 µm thick asci: clavate, 75-90 x 15-35 µm, 100-200-spored ascospores: hyaline, simple, 3.5-6 x 2-3 µm, mostly broadly ellipsoid Pycnidia: abundant, obconic to almost globular, with a pale ostiole, 180-200 x 100-180 µm conidia: short bacilliform, mostly 2 x 1 µm Spot tests: UV+ orange, all spot tests negative Secondary metabolites: epanorin (major or trace), rhizocarpic acid (major or trace), with or without conepanorin (minor) or conrhizocarpic acid (minor) or trace of vulpinic acid (HPLC, J.A. Elix, pers, comm.) The chemotypes do not appear to have a distinct geographical distribution or differences of substrate. Substrate and ecology: on volcanic or acidic rocks or on soil World distribution: South America (Argentina, Bolivia, Chile, and Peru) and central California (Diablo Peak) Sonoran distribution: southern Arizona and southern California (Santa Cruz Island). Notes: Acarospora rhabarbarina Hue is common in South America from 500-4930 meters. The species when developing a stipe on rock looks similar to A. socialis, but differs with its regularly dark red discs, with its dark capped paraphyses, and with its distinctly jagged algal layer interrupted with hyphal bands. There is much confusion about Acarospora rhabarbarina and its identity was cleared up with the help of the Paris Herbarium and Valérie Reeb as well as J.A. Elix in our progress in researching a paper on South American Acarospora (in prep.) The root of the confusion is Nylander. His concept of yellow Acarospora in South America saw no distinction between the taxa that occur there. He designated one taxon as the type when describing Lecanora bella; then, when he found that name was illegitimate because Acharius had used the name earlier, he changed it to Lecanora xanthophana but designated as the type another specimen, believing both specimens were same taxon. We do not know (nor did Magnusson) if Jatta had a real specimen of Lecanora bella when he made the combination Acarospora bella (Nyl.) Jatta. Hue obviously did not think so and described the taxon originally named Acarospora bella validly as Acarospora rhabarbarina. The author accepts this name for the taxon treated above. Based on just examining the specimens from Nylander's herbarium at H, which are very poor, the author originally thought that L. bella and L. xanthophana described the same species (Knudsen and Lendemer 2005b). Magnusson (1929) distinguished A. malmeana from other taxa based on its multiple apothecia in a wheel-like formation but this character is clearly seen integrating with single apothecium per areole in Nash #23, 897 (ASU!) from same province and area in Argentina as type locality of A. malmeana. This unusual formation occurs in A. socialis and A. chrysops on occasion. Acarospora. Terrestris (Nyl.) H. Magn. Was named from a sterile specimen. Fertile specimens collected side by side of fertile on rock and soil in Peru by Weber and Johnson (L-64272 & 64273, COLO!) confirm A. terrestris as a synonym of A. rhabarbarina as do fertile collections on soil by Robin Schroeder on Santa Cruz Island.