Magnusson, A. H. (1929). A Monograph of the Genus Acarospora (Vol. 6, No. 17). Almqvist & Wiksells Boktryckeri.
Thallus coherent, very thin, 0.2-0.3 mm, forming dark reddish-brown patches up to at least 3 cm broad, with the margin distinctly effigurate (when well developed). Lobulae closely appressed, mostly plane or somewhat convex, towards the margin very thin, about 0.2-0.3 mm broad and 0.4-0.6 mm long. The rest of the thallus verrucose, verrucae 0.2-0.5 mm large, mostly separated by cracks. Lower side dark brown. No reaction with KOH or CaCl2O2.—Upper cortex very thin, about 10 µ, exterior 4-7 µ dark brown, amorphous stratum none or up to 10 µ thick. Cortex with a yellowish shade, gelatinized, cells indistinct, about 1.5 µ in diam., the ends of the hyphae 3-4 µ thick, brown. Gonidia 6-15 µ in diam., occupying most part of the section, both upper and lower surface indistinct. Medulla very poorly developed, with densely intricate, both in HCl and KOH indistinctly observable hyphae. Lower cortex 6-15 µ thick, dark brown or blackish.
Apothecia covering most part of the thallus, as a rule solitary, at first punctiform, then impressed, disc brownish-black or black, 0.2-0.3(-0.5) mm broad, mostly regular, concave, much darker than the thallus, a little rough when old, surrounded by an obtuse margin.—Excipulum indistinct or up to 15 µ thick. Hypothecium up to 25 µ thick, with a yellowish shade. Hymenium (75-)100-135 µ high, exterior 10 µ yellowish (or dark) brown, I+ blue. Paraphyses 1-1.5 µ thick, in rich gelatin, apices not widened, brown. Asci 65 X 30 or 85-90 X 18-20 µ, swollen or elongate-clavate. Spores very small, several hundreds, 3 X 1.5 µ. One pycnidium observed, 90 µ deep, 45 µ broad, sterigmata 12 µ long, conidia 2 X 0.8 µ.
Habitat. On mica-schist-resembling rocks, most probably on the shore (in stormbältet), because associated with Rhizcoparon constrictum, an exclusive shore-lichen. Other accompanying species are: Lecanora polytropa, Physcia conf. caesia, Gyrophora erosa, Xanthoria conf. parietina.
Distribtuion. Norway. Nordland: Steigen, Laskestad and Engelö NORMAN, Four specimens (O.). Saltdalen 1822 SMRFT. (O.), “on rock by river near Skandsen,” called Lecanora molybdina β microcyclos. Troms: Tromsöen, Lanes NORMAN (O.).
A. brunneola comes near to molybdina f. microcyclos, but is clearly distinguished by its more brownish-red colour and especially by the short marginal lobes, which are much longer than broad in microcyclos and therefore can be followed a longer distance towards the centre.