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 Life habit: lichenized; Thallus: squamulose or placodioid-subfoliose, tightly to somewhat loosely attached, most species 1.5-2.5 cm wide (but some species up to 10 cm wide), usually 1-2 mm thick (some species forming mats up to 2 cm thick); lobes: usually large (compared to those of lobate species of Lecanora), very stiff; center: rimose-areolate to squamulose; upper surface: usually ± greenish yellow when fresh, to brownish or grayish, often at least partly white due to pruina, continuous to rimose, ± smooth; isidia and soredia: absent, phyllidia-schizidia: present or absent; cephalodia: absent; upper cortex: evenly very thick (compared to most lobate species of Lecanora; 50-100 µm or more), sharply delimited, without dead algal cells; inspersed with yellowish granules (soluble in K); medulla: prosoplectenchymatous, thick, chalky; hyphae: strongly conglutinated, ± thick-walled, with wide to narrow lumina; photobiont: primary one a trebouxioid alga, secondary photobiont absent; algal layer: well-delimited, continuous, rather narrow; lower cortex: absent; lower surface: pale or dark; rhizinose strands, varying from taproot-like branched cords with compact medulla and firm outer surface (Squamarina-type) to a looser rhizohyphal felt (Placidium-type), depending on the species; Ascomata: apothecial, usually laminal, circular or irregular, subimmersed to sessile, lecanorine to occasionally biatorine (varying on the same thallus); disc: mostly yellow-brown to red-brown, pruinose or not; thalline margins: prominent or not: thick, similar in structure to that of thallus algal layer: present under hypothecium, often absent from the margin; true exciple: sometimes evident externally, hyaline or ochraceous-yellowish; hymenium: gel hyaline, euamyloid; uppermost part hyaline or ochraceous-yellowish, inspersed with fine granules or (when discs pruinose) covered with coarser granules; paraphyses: septate, not (or scarcely) branched and anastomosing; hypothecium: hyaline or ochraceous-yellowish, thick; asci: ± narrowly clavate, lecanoral; wall: euamyloid; tholus: appearing uniformly amyloid and lacking non-amyloid axial body but with small ocular chamber (Hafellner 1984), and with a regular, narrowly cylindric, deeply amyloid central tube (Timdal 1991; Haugan and Timdal 1992), 8-spored; ascospores: biseriately arranged, simple, ellipsoid or cylindrical-ellipsoid or oblong, 9-15 (-19) x 4.5-7.5 µm; wall: hyaline, smooth, thin, non-halonate, not amyloid; Conidiomata: pycnidial, immersed; conidia: formed acrogenously, filiform, ± curved, c. 15-40 x < 1 µm; Secondary metabolites: cortex with usnic acids (sometimes only traces); medulla with or without beta-orcinol depsidones or (in an undescribed species) terpenoids; Geography: Northern Hemisphere in arid and semi-arid regions; Substrate: bryophytes, soil, detritus, or usually calcium-rich rock.; Notes: For an introduction to the difficult nomenclatural and taxonomic history of this genus, see Ryan and Nash (1997b); in this Flora the present treatment covers only the core group of Squamarina; the species of “sect. Petroplaca”, which have a Lecanora-type ascus (with distinct non-amyloid axial mass) will be treated in Volume II, potentially as a different genus with the Lecanoraceae. 

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© Lichen Unlimited: Arizona State University, Tempe.

Source: Lichen Flora of the Greater Sonoran Desert Region

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