Acarospora (aka “Cobblestone Lichens” or “Cracked Lichens“)
Description: Areolate to almost squamulose crustose lichens. Photobiont green (unicellular). Paraphyses mainly unbranched; asci K/I- including the thickened tip (except K/I_ blue in A. heppii).
Color: Various colors such as white, gray, brown, & brilliant yellow.
Photobiont: Green (unicellular)
Apothecia: Usually immersed in the thalli with round to irregular disks, but occasionally somewhat prominent with lecanorine margins.
Spores: Colorless, ellipsoid to spherical. Dozens to hundreds per ascus.
Chemistry: Yellow species containing pulvinic acid derivative pigments such as rhizocarpic acid in the cortex (UV+ bright orange); a few species with gyrophoric or norstictic acids.
Substrate: On rock of various kinds, usually in full sun; a few species on soil.
Lookalikes: The brown & gray species of Acarospora can resemble some Aspicilia species, but these have large spores, 8 per ascus. Polysporina & Sarcogyne have many-spored asci, but their apothecial margins are lecideine & usually carbon-black. The yellow species of Acarospora are very similar to Pleopsidium, which differs in details of the ascus. At the present time, the species limits of the North American representatives of Acarospora, especially the yellow ones, are poorly understood.
Bibliography: Lichens of North America, by Brodo, Sharnoff, & Sharnoff
Database Entry: Distance Everheart 12-23-13