Synonyms: Acarospora heufleriana var. massiliensis Harm.; Acarospora massiliensis (Harm.) H. Magn.; Acarospora perpulchra Hue
Distribution: N - TAA, Piem (Clerc & al. 1999), VA (Piervittori & Isocrono 1999), Lig. C - Sar. S - Camp (Garofalo & al. 1999, Aprile & al. 2002), Pugl (Garofalo & al. 1999).
Description: Thallus crustose, areolate, up to 5 cm in diam. Areoles angular, 0.5-2 mm wide, flat to convex, dispersed to usually contiguous, the peripheral ones sometimes slightly elongated, corticate, bright to dull yellow. Medulla white, prosoplectenchymatous; algal layer continuous. Apothecia lecanorine, 0.3-1 mm across, 1-5 per areole, immersed, at first punctiform then expanded, with a round to irregular, reddish brown disc and a thin, inconspicuous thalline margin. Epithecium yellowish, weakly conglutinate, 10-15 µm thick; hymenium colourless, 80-135 µm high, I+ deep blue; paraphyses 1-1.8 µm thick at base; hypothecium colourless. Asci >100-spored, clavate, the apical dome K/I-. Ascospores 1-celled,: hyaline, ellipsoid to subglobose, 3-4.5 x 2-3 µm. Pycnidia globose, immersed, the ostiole visible as a pale brown dot. Conidia bacilliform, 3-4 x 1(-1.5) µm. Photobiont chlorococcoid. Spot tests: upper cortex and medulla K+ yellow turning red (often forming crystals), C- KC- P-, UV+ orange. Chemistry: rhizocarpic and norstictic acids.
Note: on horizontal to gently sloping faces of base-rich or weakly calciferous siliceous rocks near the ground in open habitats, especially in grasslands, sometimes starting the life-cycle on other crustose lichens, especially Lecanora valesiaca. Restricted to dry-continental areas, both in the Alps and in the Mediterranean Region. See also note on A. lavicola.
Growth form: Crustose
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)