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Page number:94 
Remarks (internal):Caloplaca pusilla is characterized by a placodioid, yellow ochre, pinkish or salmon colored thallus with long and ± convex marginal lobes that are tightly attached to the substratum.
Caloplaca pusilla, which was was treated as a synonym of C. saxicola for many years, has been just recently recovered as independent by Gaya (2009). Caloplaca saxicola differs from C. pusilla by an epruinose thallus with short to strongly reduced lobes that ascend distinctly from the rock, apothecia that are initially immersed in thallus and form finely, bigger and strongly aggregated clusters. The spores of C. saxicola are longer and narrower than in C. pusilla. To distinguish C. pusilla from C. pseudofulgensia, see remarks under that species.
Caloplaca pusilla often grows together with C. arnoldii (Wedd.) Zahlbr. and C. clauzadeana (Gaya) Nav.-Ros. & Cl. Roux. In comparison to C. pusilla, C. arnoldii has a distinctly reddish and smaller thallus, whereas C. clauzadeana has strongly convex lobes with yellowish tips and much narrower ellipsoid spores. For more details see Gaya (2009).
Description type:Non-original description 
Description:Caloplaca pusilla (A. Massal.) Zahlbr., Annal. Naturhist. Hofmuseums Wien 4: 353 (1889).
Thallus placodioid, rosettes 2-10 mm in diam., 0.3-0.4 mm thick, single or usually forming bigger congregations, yellow ochre, pinkish or salmon, often whitish in the centre (Séguy 1936, color codes: 185, 189-190, 203, 205, 215), surface white pruinose, especially in the centre of thallus, where necrosis may also occur; without prothallus and vegetative propagules. Marginal lobes 0.5-2 mm long and 0.2-0.5 mm wide, closely adjacent to each other or sometimes overlapping, convex or flat and broad at tips. Internal areoles convex, rounded to elongated, or areoles absent and lobes forming from the centre. Thallus cortex thin to thick, 13-80 µm, scleroplectenchymatous, without necral layer; layer of algae not continuous; medulla loose, with or without crystals. Apothecia zeorine or pseudolecanorine, abundant, in centre of thallus, crowded or scattered, immersed at first, then sessile and often constricted at the base, rounded or angular by compression, 0.2-1 mm diam.; disc flat or slightly convex, dark orange, brownish orange or blood-red, more rarely reddish orange (Séguy 1936, color codes: 126, 161, 168, 171, 186, 202, 247), sometimes slightly white pruinose; proper margin persistent, slightly raised or level with disc, concolorous with disc or slightly paler; thalline margin persistent or disappearing, sometimes heavily white pruinose. Parathecium thin, 30-42 µm, sclero-prosoplectenchymatous. Amphithecium with numerous algae in groups or forming a continuous layer, sometimes amphithecial hyphae loose, cortex thick, with crystals. Epihymenium granular, brown or reddish golden. Hymenium hyaline, 60-90 µm tall. Paraphyses simple or slightly branched, 1-2(-4) apical cells thickened, up to 8(-10) µm wide. Hypothecium hyaline, without oil droplets and crystals, prosoplectenchymatouseous. Asci 8-spored, spores polaribilocular, thin-walled, 8.5-15 x 4-8.5 µm, isthmus 2.5-5 µm wide. Pycnidia infrequent, inconspicuous, immersed; conidia colorless, ellipsoid to bacilliform, 3 x 1.5 µm.
Spot test reactions: thallus K+ purple, J-, N-, medulla K-, J-, N-, epihymenium K+ purple.
Distribution and ecology - The widely distributed Caloplaca pusilla is probably cosmopolitan (Gaya 2009). The species grows on natural calcareous rocks and mortar, is known from varying altitude and exposures, and prefers eutrophic environments. It is characteristic of the association Caloplacetum pusillae Du Rietz ex Kaiser 1926 but may also be found in the Caloplacetum arnoldii association (see Gaya 2009).
The species, which appears widely distributed in Poland, was found in the Carpathians (Gorce and Pieniny Mts) and in the lowlands in Warmian- Masurian province. More herbaria materials need revision to determine the true distribution, because C. pusilla has previously been filed under the name C. saxicola (Fa?tynowicz 2003). In Poland the species occurs on limestone, calcareous sandstones, and (commonly) concrete in sunny sites at up to 980 m.
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