Herzogia, 5: 59, 1979. Basionym: Buellia subcanescens Werner - Bull. Soc. Hist. Nat. Afrique du Nord, 47: 90, 1956.
Synonyms: Buellia leptina J. Steiner
Distribution: C - Tosc (Brackel 2015), Sar (Rizzi & al. 2011). S - Bas (Potenza 2006, Potenza & al. 2010, Potenza & Fascetti 2012), Cal (Puntillo 1996), Si (Ottonello & Romano 1997, Ottonello & al. 2011).
Description: Thallus crustose-placodioid, glaucous white, often at least partly slightly pruinose at lobe-tips, forming 1-5 cm wide, usually orbicular rosettes, sometimes several thalli merging and covering larger surfaces. Lobes radiating, contiguous, slightly convex, rounded and often slightly broader and fan-shaped at ends, esorediate; lower surface usually pale, attached by medullary hyphae. Upper cortex pseudoparenchymatous, formed by vertically arranged hyphae, filled with minute crystals not dissolving in K; medulla usually white, lax. Apothecia frequent, lecideine, black, up to 1 mm across, laminal. Proper exciple thin and becoming excluded with age; epithecium granular, brown-black, K-; hymenium colourless; paraphyses simple to sparingly branched, the apical cells enlarged; hypothecium brown or brown-black. Asci 8-spored, clavate, Lecanora-type. Ascospores 1-septate, brown, thick-walled, ellipsoid, 9-12 x 5-8 µm, Dirinaria-type, with ontogeny of type B (apical inner wall-thickenings produced before septum formation). Pycnidia laminal, immersed. Conidia hyaline, simple, rod-shaped, 5-8 µm x c. 1 µm. Photobiont chlorococcoid. Spot tests: cortex K+ yellow, C- or C+ fleeting pink, KC+ pale yellow to yellow-orange, P-; medulla K-, C+ fleeting pink, KC+ fleeting pink, P-, UV+ dull orange. Chemistry: cortex with atranorin and often chloroatranorin, medulla with diploicin (major), gyrophoric acid, and other minor compounds.
Note: a southern Mediterranean-Atlantic lichen found on siliceous rocks subject to humid, maritime winds, exclusively Tyrrhenian in Italy. Although there is some molecular evidence (Molina & al. 2002) that this is a synonym of D. canescens, I am not yet convinced (see also Roux & coll. 2014), and I prefer to maintain D. subcanescens as distinct from D. canescens.