(in Vondrák & al.) J. System. Evol., 2019 (in press).. Basionym: Lecanora ferruginea var. festivella Nyl. - Flora, 56: 197, 1873.
Synonyms: Lecanora limitosa Nyl.; Caloplaca festiva var. decussata (Bagl.) H. Olivier; Caloplaca festivella (Nyl.) Kieff.; Caloplaca limitosa (Nyl.) H. Olivier ?
Distribution: N - Piem (Favero-Longo & al. 2015), Lig (LD-1011409). C - Tosc, Sar (Nöske 2000). Si.
Description: Thallus crustose, episubstratic, grey, thin to moderately thick, areolate, delimited by a conspicuous black prothallus. Areoles contiguous, flat to strongly convex, smooth or uneven. Apothecia biatorine/zeorine, 0.6-1.3 mm across, with a flat to slightly convex, red to rust-red disc, and an often blackened proper margin, the blackened parts K-, N+ violet. Proper exciple prosoplectechymatous; epithecium orange-brown, K+ red; hymenium colourless, not inspersed with oil droplets; algal layer not present below the hymenium; paraphyses 1.5-3 μm thick in lower part, the apical cells only slightly wider; hypothecium colourless. Asci 8-spored, clavate, Teloschistes-type. Ascospores 1-septate, polarilocular, hyaline, ellipsoid, 11-17.5 x 6-8 μm. Pycnidia dark grey, with the Cinereorufa-green pigment, rarely with anthraquinones. Conidia bacilliform, rarely narrowly ellipsoid, 3-5 x 1-1.5 μm. Photobiont chlorococcoid. Spot tests: prothallus, pycnidial wall and often margin of apothecia K-, N+ violet (in section); apothecia K+ red. Chemistry: non-chlorinated anthraquinones in apothecial disc, chlorinated anthraquinones in exciple; Cinereorufa-green pigment in prothallus, pycnidial walls and sometimes apothecial margin.
Note: a Mediterranean-Macaronesian lichen found on hard siliceous rocks, from granite to basalt, usually (but not always) not far from the coast, exclusively Tyrrhenian in Italy. The species could be identical with Caloplaca limitosa, in which case the epithet limitosa would have priority (Vondrák & al. 2020). Earlier records from Calabria (Nimis 1993: 167) refer to B. gennargentuae.