Description ⁶

 Thallus: rimose-areolate, indeterminate, continuous, overall up to 4 cm wide; areoles: angular, contiguous, rarely subeffigurate with some shallow irregular lobes on edge (in one high elevation specimen), usually 0.2-0.5(-1) mm wide, often very thin, less than 0.4 µm thick; rim: lacking; upper surface: yellow, plane, smooth, dull, epruinose; cortex: paraplectenchymatous, 25-40 µm thick; syncortex: thin; eucortex: opaque yellow above; hyaline below; algal layer: dense to thin, with uneven upper and lower borders; medulla: white, prosoplectenchymatous; attachment: broad, without a stipe; Apothecia: one or more per areole, immersed, below or even with upper surface, 0.1-0.3 mm in diam.; disc: blackish to reddish brown, concave to plain, round to irregular in shape, often with interascal sterile plectenchyma that is eventually dissolved, occasionally with a thalline collar pushed up by expansion of the apothecium; parathecium: narrow to wide, c. 50 µm thick, but can expand to form parathecial crown; epihymenium: dark brownish yellow, 15-30 µm thick; hymenium: hyaline to pale yellow, 85-125 µm tall; paraphyses: coherent, 1.6-1.9 µm in diam. at base, apices slightly expanded; subhymenium: hyaline, 25-30 µm thick; hypothecium: hyaline, 50-100 µm thick; asci: clavate, 60-80 x 16-23 µm, 100+-spored; ascospores: hyaline, simple, narrowly ellipsoid, 4-5 x 1.7-1.9 µm; Pycnidia: not seen; Spot tests: UV+ orange, all spot tests negative; Secondary metabolites: rhizocarpic acid.; Substrate and ecology: on acid rocks from 500 meters in elevation to c. 3350 m; World distribution: western North America (Arizona to Texas), Mexico; Notes: Acarospora contigua is easily identified by its epruinose, rimose-areolate thallus, but it can be confused with other species, like A. socialis, which have an areolate stage in their development, or with the effigurate species when the edge is missing. A Darrow collection (ASU) from the San Francisco Peaks developed as a subsquamulose thallus with subeffigurate margins when coming into contact with other crustose lichens; otherwise, on a smooth surfaces, it developed without an effigurate margin. Few specimens were seen during this study and this species needs a more extensive investigation. It is a yellow equivalent of A. scotica. Golubkova's (1983) use of A. contigua, reflected in Lichens of North America (Brodo et al. 2001) with Roux determining an Acarospora species from Ozarks as A. contigua, is rejected in this treatment as not being consistent with the type. Some of her work does not transcend Magnusson's treatments and adopts too literal a dependence on Magnusson's keys and descriptions. 

Sources and Credits

1. (c) Richard Droker, some rights reserved (CC BY-NC-ND), https://www.flickr.com/photos/29750062@N06/20238137691/
2. (c) Richard Droker, some rights reserved (CC BY-NC-ND), https://www.flickr.com/photos/29750062@N06/20224083692/
3. (c) Jason Hollinger, some rights reserved (CC BY), https://upload.wikimedia.org/wikipedia/commons/9/91/Gold_Cobblestone_Lichen_%281247144434%29.jpg
4. (c) Jason Hollinger, some rights reserved (CC BY), https://upload.wikimedia.org/wikipedia/commons/6/65/Brown_Tile_and_Gold_Cobblestone_Lichens_%285037667763%29.jpg
5. (c) Jason Hollinger, some rights reserved (CC BY), https://upload.wikimedia.org/wikipedia/commons/d/d2/Gold_Cobblestone_Lichen_%284974856094%29.jpg
6. (c) Lichen Unlimited: Arizona State University, Tempe., some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/10549134

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