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 Thallus: thinly areolate, indeterminate, overall up to 6 cm wide; areoles: usually sharp-edged, angular, up to 0.5 mm in diam., 0.1-0.3 mm thick, imbricate; rim: plane, ±black, ±down-turned; upper surface: dark brown, dull, smooth, fissured or not, epruinose; upper cortex: paraplectenchymatous, (10-)15-30(-40) µm thick; cells: round to irregular, 3-5 µm wide; syncortex: very thin or absent; eucortex: upper layer brown and c. 10 µm thick, lower layer hyaline and 10-30 µm thick; lateral cortex: thinner than upper cortex; algal layer: ±100 µm, algal cells usually ±10 µm in diam., forming an uneven stratum, the algal stratum interrupted by hyphal bands; medulla: white, prosoplectenchymatous; lower cortex: lacking or narrow around attaching hyphae, up to ten cells thick beneath rim; lower surface: white or pigmented brown or black; attachment: broadly attached, never forming a stipe or areoles becoming elevated; Apothecia: usually one per areole; disc: usually dark brown when dry, 0.1-0.2(-0.5) mm in diam.; punctiform; parathecium: c. 10 µm thick, sometimes visible at surface as thin margin around disc, almost non-existent in smallest apothecia; epihymenium: pale yellow to dark brown, c. 10µm thick; hymenium: hyaline, 50-100 µm tall; paraphyses: (1.3-)1.5-1.7(-2.1) µm wide at base, apices usually not expanded; coherent in gel dissolving in K; subhymenium: hyaline, gray, or pale yellow, 15-50 µm thick; hypothecium: indistinct, c. 10 µm thick; asci: clavate, c. 70 x 10-15(-25) µm, 100+-spored; ascospores: hyaline, simple, ellipsoid, (3-)4-5 x 1.5-1.7(-2.2) µm; Pycnidia: not seen; Spot tests: UV-, all spot tests negative; Secondary metabolites: none detected.; Substrate and ecology: on granitic and volcanic rocks; lichenicolous, observed growing out of the thallus of Aspicilia; World distribution: Europe, North America, and Mexico; Sonoran distribution: Arizona and southern California.; Notes: The circumscription of A. scotica here does not follow the circumscription of Clauzade et al. (1981). Acarospora scotica looks like a Staurothele and is often sterile. It occurs in small amounts in many lichen communities and can often be spotted in packets of other genera. But it is rarely collected separately, except when its thallus is well-formed and extensive. It becomes dispersed on rough surfaces, leading to specimens Magnusson recognized as other species (see the synonyms given above). Sometimes it can be confused with immature thalli of A. badiofusca or other species in a young thin spreading areolate stage. Acarospora complanata H. Magn. is not considered a synonym of A. scotica or as occurring in North America. This author considers A. complanata a distinct C+ red species occurring in Europe, based on study of type (UPS!). The species needs further investigation. 


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© Lichen Unlimited: Arizona State University, Tempe.

Source: Lichen Flora of the Greater Sonoran Desert Region

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