Thallus: tightly adnate, up to 3 cm across, up to 1-2 mm thick, ± distinctly rosetted, not imbricated, not mat forming; thallus center: areolate lobes: 2-4 mm long, 0.5-2 (-3) mm wide, coarsely crenate-incised; edges: raised and thickened areoles: plane to convex, 0.5-1 mm across, sometimes strongly wrinkled to verrucose (partly due to abundant apothecial primordia) upper surface: pale or light greenish yellow to grayish greenish yellow, mostly epruinose except on lobe edges, or appearing yellowish white from pruina, especially on lobe edges and spottily in thallus center, sometimes wrinkled, especially in thallus center upper cortex: c. 50 µm thick, ± gelatinized, of mostly anticlinal hyphae; epinecral layer c. 10 µm thick medulla: with grayish granules (insoluble in K); algal layer: c. 30 µm thick [up to 50 µm or more in non-Sonoran material], ± continuous; algae c. 10-12 µm diam. lower surface: pale, rarely darkening; rhizinose strands: rather few and inconspicuous, 0.5 mm long, Psora-type (intermediate between Squamarina-type and rhizohyphal felt) Apothecia: usually common and crowded in thallus center, up to 1 mm diam., but often smaller; disc: epruinose, plane to slightly convex, moderate orangish yellow, yellowish brown or with pinkish-orange tinges, sometimes darkened by parasites, plane to convex; thalline margin: 0.1 mm wide, entire, pruinose, soon excluded; amphithecial hyphae: radially arranged; algal layer: mainly below hypothecium, thick, continuous; true exciple: not evident externally; hymenium: c. 65-75 µm high, uppermost c. 10-20 µm pigmented; paraphyses: ± loosely coherent, c. 2-2.5 µm thick; tips: hyaline, little thickened; hypothecium: of unoriented hyphae asci: narrowly clavate, c. 35-45 x 10-12 µm, 8-spored ascospores: mostly immature, in ascus ellipsoid, 10 x 4.5 µm [mature spores in non-Sonoran material c. 8-12 x 5-6 µm] Pycnidia: uncommon or inconspicuous; ostioles: yellowish to dark olivaceous brown conidia: c. 18-35 x < 1 µm [based on non-Sonoran material] Spot tests: cortex: K+ yellow or K-, C-, KC+ yellow, P-; medulla: K-, KC-, C-, P- or P+ yellow Secondary metabolites: cortex: with usnic acid (major), and sometimes also isousnic acid (minor); medulla: with or without psoromic acid chemosyndrome or various unidentified substances; psoromic and non-psoromic chemotypes present in the Sonoran region and other warm areas; reports of atranorin (e.g., by Hale 1979) are apparently based on misidentification of isousnic acid. Substrate and ecology: on sandy, calcareous soil in arid areas, montane World distribution: Europe, Asia, North America Sonoran distribution: northern Arizona, 910-1615 m. Notes: Although the map in Hale (1979) suggests that the species extends into southern California, I have seen no material of Squamarina s. str. from that state. As discussed by Ryan and Nash (1997b), Röser (1996) and Feige et al. (1997), this species includes specimens with P+ yellow medulla (psoromic acid), which in China has gone under the name of S. kanusensis. Although the species can be rather variable and sometimes problematic (especially in more northern parts of North America), the limited amount of Sonoran material seems to be rather uniform and quite similar in morphology and anatomy to most European material.