Circinaria hoffmanniana (S. Ekman & Fröberg ex R. Sant.) A. Nordin
in Roux & al., Bull. Soc. linn. Provence, 67: 179, 2016.. Basionym: Aspicilia contorta subsp. hoffmanniana S. Ekman & Fröberg ex R. Sant. - Lichens and Lichenicolous Fungi of Sweden and Norway: 23, 1993.
Synonyms: Aspicilia caesioalba (Le Prévost) Hue; Aspicilia hoffmanniana (S. Ekman & Fröberg ex R. Sant.) Cl. Roux & M. Bertrand; Aspicilia hoffmannii auct. non (Ach.) Flagey; Circinaria contorta subsp. hoffmanniana (R.Sant.) I. Zhdanov; Circinaria contorta subsp. hoffmanniana (R.Sant.) I. Zhdanov; Lecanora calcarea var. hoffmannii (Ach.) Sommerf.; Lecanora hoffmannii (Ach.) Müll. Arg.; Pachyospora calcarea f. cinereovirens A. Massal.?
Description: Thallus crustose, episubstratic, areolate, grey or grey-brown, grey-green in some forms, dull, forming regular, usually well-delimited, 1-8(-20) cm wide patches. Areoles usually angular or irregular, flat to weakly convex, 0.3-1.5 mm in diam., contiguous and separated by cracks. Apothecia lecanorine-aspicilioid, 0.2-0.5(-0.8) mm across, 1(-3) per areole, round, rarely angular, with a black, but usually white-pruinose, concave to flat disc and a distinctly raised, often white-pruinose thalline margin. Epithecium olive green to olive-brown, with crystals, N+ green, K+ brown; hymenium colourless, I+ blue or sometimes partly turning yellow-green; paraphyses slightly branched and anastomosing, 1.5-2.5 µm thick at base, submoniliform in upper part, the uppermost cells subglobose, (3-)4-6 µm wide; subhymenium and hypothecium colourless. Asci (2-)4(-6)-spored, clavate, the thin outer coat K/I+ blue, the wall and apical dome K/I-. Ascospores 1-celled, hyaline, globose to subglobose, (16-)18-28(-35) x (14-)17-26(-30) µm. Pycnidia rare, immersed, with a black, punctiform ostiole. Conidia filiform, straight or slightly curved, (5-)6-10(-11) x 0.8-1(-1.3) µm. Photobiont chlorococcoid. Spot tests: cortex and medulla K-, C-, KC-, P-. Chemistry: usually with aspicilin, rarely lacking secondary metabolites.
Note: an early coloniser of a wide variety of calciferous or base-rich substrata, from limestone and dolomite to brick, roofing tiles and mortar walls; one of the most frequent taxa of the genus in Italy, occurring also inside large urban areas, with optimum below the montane belt. Since a molecular study of the complex is in progress, I refrain from a formal recombination. See also notes to C. contorta subsp. contorta and to C. viridescens.