Acarospora marcii H. Magn.

K. svenska Vetensk-Akad. Handl., Ser. III, 7, 4: 305, 1929.
Distribution: N - TAA (B 189317), VA (B-189320). C - Sar.
Description: Thallus crustose, episubstratic, pale to dark brown, dull, epruinose, areolate-subsquamulose, the areoles 0.5-1.5 mm wide, 0.3-0.5 mm thick, convex, angular, broadly attached. Epicortex 10-20 µm thick; cortex 11-25(-40) µm thick, dark reddish brown in upper part, otherwise colourless, prosoplectenchymatous above interrupting hyphal bundles, the cortical cells (1.5-)2(-3) µm wide; algal layer 100-200 µm thick, continuous or interrupted by 20-30 µm wide hyphal bundles; medulla 200-300 µm thick, mostly dark at base. Apothecia immersed in the areoles, 1-4 per areole, 0.2-0.4 mm across, with a strongly concave, crateriform, epruinose disc. Proper exciple distinct, 10-40 µm thick; epithecium brown; hymenium colourless, 90-100 µm high, hemiamyloid, K/I+ blue slowly turning dirty reddish; paraphyses coherent, branched, c. 2 µm thick, the apical cells up to 3 µm wide, with brown gel caps; subhymenium ca.40 µm tall, K/I+ dark blue; hypothecium c. 10 µm high. Asci c. 200-spored, cylindrical-clavate, the apical dome K/I-. Ascospores 1-celled, hyaline, narrowly ellipsoid, 3-5 x 1.5-1.7 µm. Photobiont chlorococcoid. Spot tests: cortex and medulla K-, C+ red, KC+ red, P-. Chemistry: gyrophoric acid.
Note: on exposed surfaces of siliceous rocks in eutrophicated situations. A rather poorly-known and often misunderstood taxon. Clauzade & Roux (1985) considered it as a synonym of A. peliscypha, while Roux & al. (2019) synonymised it with A. hellbomii. According to Knudsen (in litt.), on the contrary, this is a well-distinct species.
Growth form: Crustose
Substrata: rocks
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly sexual
Species of metal-rich rocks

Commonnes-rarity: (info)

Alpine belt: very rare
Subalpine belt: very rare
Oromediterranean belt: very rare
Montane belt: very rare
Submediterranean belt: absent
Padanian area: absent
Humid submediterranean belt: absent
Humid mediterranean belt: absent
Dry mediterranean belt: absent

pH of the substrata:


Solar irradiation:








Altitudinal distribution:


Predictive model