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Page number:91 
Remarks (internal):Caloplaca oasis is characterized by a reduced thallus and small dark orange apothecia with thin proper margins.
Arup (2009), who discusses the species in detail in the recent monograph on the C. holocarpa group, notes that C. oasis has been often misidentified as C. holocarpa (Ach.) A.E. Wade, especially when growing on anthropogenic substrates. However, C. holocarpa produces more yellow-tinged apothecia with thicker, more prominent proper margins and spores with a broader isthmus (see Arup 2009). Well-developed parasitic C. oasis specimens may also be confused with C. polycarpa (A. Massal.) Zahlbr., which can be distinguished by larger apothecia with thicker margins and more distinct, thicker orange thalli (see Arup 2009 for more details).
 
Description type:Non-original description 
Description:Caloplaca oasis (A. Massal.) Szatala, Magyar Bot. Lapok 31: 120 (1932).
Thallus strongly reduced and only some small granules or areoles visible at thallus margin, pale yellow (Séguy 1936, color code: 290), rounded in shape; without prothallus and vegetative propagules. Apothecia pseudolecanorine or zeorine, abundant, crowded, sessile, round or angular by compression, 0.1-0.3 mm diam.; disc flat or slightly convex, orange (Séguy 1936, color codes: 196, 211), epruinose; proper margin very thin, not prominent, slightly raised or level with disc, smooth, concolorous with or slightly paler than disc; thalline margin much reduced, only in young apothecia visible. Parathecium thin, ca. 60 µm, prosoplectenchymatous, hyphae radiating with oval to elongated cells. Amphithecium ±reduced, with numerous algae, cortex poorly developed. Epihymenium granular, yellow. Hymenium hyaline, 75-85 µm tall. Paraphyses simple or slightly branched above, 1-2 apical cells thickened, up to 7 µm wide. Hypothecium hyaline, without crystals or oil droplets, prosoplectenchymatous, hyphae irregular, ca. 40-50 µm high. Asci 8-spored, spores polaribilocular, thin-walled, 8.5-13.5 x (4.0-)4.8-6.8 µm, isthmus 3-5 µm wide. Pycnidia not observed.
Spot test reactions: thallus K+ purple, medulla K-, epihymenium K+ purple.
Distribution and ecology - Caloplaca oasis, which is widespread in Europe (Arup 2009), is also reported from Western Asia (John et al. 2004) and North Africa (Thor & Nascimbene 2010). The species grows mainly on pure limestone, concrete and mortar (Arup 2009), where it occurs as free living or a parasitic lichen growing on endolithic Verrucaria s. lat. The species is characteristic for the associations Aspicilietum calcareae Du Rietz 1925 emend. Roux 1978 and Caloplacetum citrinae Beschel ex Klement 1955.
The species was found in the Carpathians (Gorce Mts) at elevations up to 550 m and in the Pomeranian lowlands, where it grows on calcareous sandstones and concrete. This is the first report of the species from Poland.
 
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