Type: U.S.A., New Mexico, Las Vegas, ca. 2000 m, on sandstone, A. Brouard 19885 (Hb. B. de Lesdain, presumed lost; isotype, UPS).
Description.Thallus of squamules 0.5-1.5 mm wide, 0.2-0.5 mm thick. Upper surface light to dark brown, usually densely pruinose, rarely with a few intermixed non-pruinose squamules, forming fissures and replicating by division, usually forming groups up to 1 cm across. Lower surface ecorticate, pale or brownish from substrate interactions. Epicortex 10-30 µm thick. Upper cortex 20-30 µm thick, cells 3-5 µm wide, algal layer 60-100 µm thick, algal cells 6-12 µm in diameter. Medulla poorly developed and of narrow hyphae continuous with stipe. Apothecia usually one per squamule (rarely two), 0.7 mm or less in width, immersed, dark brown, usually epruinose. Parathecium indistinct. Hymenium mostly 80-90 µm tall, epihymenium 10 µm tall, paraphyses mostly 2-2.5 µm wide at midlevel, hymenial gel IKI+ greenish blue turning red or red (hemiamyloid). Asci mostly 50-60 × 14-16 µm, ascospores variable but mostly narrow ellipsoid, 3-5 × 1.5-2.0 µm. Subhymenium 30-45 µm tall, IKI+ blue. Hypothecium indistinct. Pycnidia not observed. Not producing secondary metabolites.
Ecology and distribution. Usually in full sun on acidic sandstone, rhyolite, or granite, infrequent from California to New Mexico in the Mojave, Sonoran, and Chihuahuan Deserts extending north to at least Oklahoma and Wyoming.
Discussion. The species in Sonoran flora was treated as a synonm of A. veronensis but it was removed from synonymy by Knudsen in 2011. It differs from A. veronensis in forming a stipe. There is an undescribed species that can become densely pruinose and looks similar, but it produces gyrophoric acid and lacks a stipe. It can also be confused with A. nicolai H. Magn. which also is heavily pruinose and produces gyrophoric acid.