Distribution: C - Sar (Crespo & al. 2004). S - Si (Nimis & al. 1994, Ottonello & Salone 1994, Crespo & al. 2004).
Description: Thallus crustose-placodioid, bluish white- to grey-pruinose, sorediate, forming orbicular, up to 3(-5) cm wide rosettes which are often confluent, covering large surfaces. Central parts areolate, marginal lobes contiguous to laterally subimbricate, 1-5 mm long, (0.3-)0.5-1 mm wide, the tips only slightly widened. Soralia arising on the lobe surface, small (c. 0.2-0.3 mm across), circular, well-delimited by a thin thalline margin, often raised, with granulose, 50-55(-90) μm wide soredia more or less concolourous with thallus, covered with a layer of brownish angular cells and a variably developed layer of minute colourless crystals. Cortex covered and interspersed with coarse crystals, of hyphae arranged perpendicularly to the surface, the upper 1-3 cells brownish and ca 3.5 μm wide; medulla white, I-. Apothecia unknown. Pycnidia dark, immersed, globose, with pleurogenous conidogenous cells. Conidia cylindrical, 3.8-5 x c. 1.3 μm. Photobiont chlorococcoid. Spot tests: cortex and medulla K-, C-, KC-, P-, UV- or UV+ pale yellow. Chemistry:thallus with low amounts of zeorin plus sometimes an unknown substance.
Note: a mainly western, Mediterranean-Atlantic species growing on soft calcareous rocks wetted by rain and exposed to humid maritime winds, mostly on horizontal surfaces, often forming large monospecific stands. It is locally abundant along the western coasts of Sicilia and Sardegna.
Growth form: Crustose placodiomorph
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)