Synonyms: Placodium chlorophanum var. hilare (Dufour) Boistel
Distribution: C - Tosc (Tretiach 1993), Sar (Tretiach 1993). S - Cal (Puntillo 1996), Si (Nimis & al. 1996b, Grillo & Caniglia 2004).
Description: Thallus crustose-placodioid, episubstratic, bright lemon yellow, slightly glossy, epruinose, forming orbicular to irregular, often confluent rosettes covering wide surfaces. Central parts of thallus of contiguous, angular, flat to slightly convex areoles; marginal lobes radiating, flat or very slightly convex, 1-2(-4) x 0.3-0.6(-1) mm. Medulla white; algal layer continuous. Apothecia lecanorine, immersed in the areoles (1-3 per areole), with a punctiform, dark brown disc and a poorly evident thalline margin. Epithecium brownish; hymenium colourless, 85-100 µm high; hypothecium colourless. Asci 100-200-spored, broadly ellipsoid, the apical dome K/I-. Ascospores 1-celled, hyaline, ellipsoid, 3-6 x 2 µm. Photobiont chlorococcoid. Spot tests: corte and medulla K-, C-, KC-, P-. Chemistry: cortex with rhizocarpic acid.
Note: a xeric subtropical species found on vertical to underhanging faces of hard siliceous rocks which are rarely wetted by rain, restricted to the driest parts of Mediterranean Italy. Chemically heterogeneous (epanorin or rhizocarpic acid).
Growth form: Crustose placodiomorph
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly sexual
Subcontinental: restricted to areas with a dry-subcontinental climate (e.g. dry Alpine valleys, parts of Mediterranean Italy)