Thallus: foliose, orbicular to irregularly spreading, loosely attached centrally, with free apices, 2-6(-8) cm in diam., rather coriaceous; lobes: broadly rounded, 10-30 mm in diam., discrete to shallowly overlapping at margins, complex-folded centrally; margins: entire with a distinct, slightly raised, thin, black or dark brown rim below, occasionally with a bristle appearance due to phyllidia; upper surface: centrally dark blue-black or glaucous blue-gray when moist, pale blue-gray or fawn-colored, marginally often suffused dull charcoal gray to blue-gray when dry, smooth, undulate to shallowly wrinkled or subfaveolate in parts, dull, delicately white-pruinose to minutely white-pilose at margins or around apothecia (x10 lens), with minute, white, scattered maculae best seen when moist (x10 lens), without isidia or soredia, occasionally phyllidiate; phyllidia: marginal and laminal, regenerating from cracks and tears in upper surface, flattened, dorsiventral, with minute cyphellae developing on the lower surface, coralloid-branched, 0.2-1(-2) mm tall; medulla: white; photobiont: cyanobacterial; lower surface: pale buff or cream-colored marginally to dark red-brown centrally, moderately to thickly tomentose from margins to center; tomentum: short and velvety, to long and shaggy; cyphellae: pale buff or cream-colored, scattered, moderately common, pin-prick-like at margins, round to irregular, 0.1-1(-2) mm in diam., rather flat, with very thin, slightly raised margins, often obscured by tomentum, with a brilliant-white basal membrane; Apothecia: occasional to absent, generally best developed and clustered at or near margins (similar to S. tomentosa), sessile, constricted at base, round, 1-2.5(-3.5) mm in diam.; disc: pale to dark red-brown, dull, deeply cupuliform at first and obscured by massive margin, soon becoming plane to shallowly convex at maturity, epruinose; margin: pale pinkish buff to fawn, coarsely corrugate-scabrid, persisting at maturity, prominent, toothed to stellate, often with projecting tufts of brown rhizines; epihymenium: pale yellow-brown, 10-15 µm thick; hymenium: hyaline, 85-115 µm tall; hypothecium: opaque pale orange-brown, 40-100 µm thick; asci: clavate, 80-90 x 12.5-17.5 µm; ascosopores: hyaline, 1-3septate, fusiform-ellipsoid with pointed apices, vacuolate, 28-32 x 5-7 µm; Pycnidia: occasional to rare, developed towards margins, immersed but apparent as distinct, pale buff or brownish swellings, 0.2-0.5 mm in diam., with a central, depressed red-brown to brown-black ostiole; conidia: bacilliform, straight, with slightly swollen apices, 3-5 x 1 µm; Spot tests: all negative; Secondary metabolites: none detected.; Substrate and ecology: in mixed pine and oak forest, on bark of Quercus and amongst mosses on rhyolite and other acid rocks, 1700-2300 m; World distribution: only known from Mexico, including Durango; Sonoran distribution: occasional to moderately common in Chihuahua, and Sinaloa.; Notes: Sticta nashii is similar in gross morphology to S. tomentosa, but differs in having: flattened, coralloid phyllidia produced at the lobe margins and along superficial cracks and tears on the upper surface; small bundles of dark-brown or red-brown rhizines developed here and there along lobe margins, sometimes intermixed with the phyllidia and producing a "bristling" appearance to the margins; and having apothecial margins notably ragged-stellate and with the margin below the disc being coarsely corrugate-scabrid (not velvety-pilose as in S. tomentosa) with projecting tufts of coarse rhizines often developed in both young and mature apothecia. Both fresh and dried specimens smell strongly of amines (fishy).
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