Synonyms: Bacidia arenicola (Nyl. ex Mudd) H. Olivier; Bacidia flavovirescens var. arenicola (Nyl. ex Mudd) A.L. Sm.; Gongylia sabuletorum (Fr.) Stein; Gongylia viridis A.L. Sm.; Lahmia fueistingii Körb.; Mycobacidia arenicola (Nyl. ex Mudd) Sacc. & D. Sacc.; Raphiospora arenicola Nyl. ex Mudd; Sagedia sabuletorum (Fr.) A. Massal.
Distribution: N - TAA.
Description: Thallus crustose, episubstratic, dark grey-green, thin, developing on the thalli of Baeomyces-species, immersed in the thallus of the host and appearing as a dark spot. Apothecia lecideine, black, 0.2-0.5 mm across, sessile, not constricted at base, with an initially urceolate, then concave to finally flat, smooth disc, and a thick, rugose, persistent proper margin. Excipulum dark brownish green in the outer and innermost parts, paler inbetween; epithecium brownish to greenish brown, K-; hymenium colourless, inspersed with oil droplets, I ; paraphyses slender (to 2 μm thick), branched and anastomosing, not thickened at apex, free; hypothecium brown in lower part.. Asci 8-spored, subcylindrical to clavate, the wall of young asci with a poorly developed tholus and an ocular chamber, that of mature asci more or less uniformly thick throughout. Ascospores (8-)12-15-septate, hyaline, acicular, thin-walled, (20-)30-70(-90) x 2-3.5(-4) μm. Photobiont chlorococcoid. Spot tests: K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: an arctic-alpine species found on soil and weathered siliceous rocks near and above treeline, first parasymbiotic on Baeomyces (Baeomyces carneus, B. rufus and, more rarely, B. placophyllus), later an autonomous lichen. The species is known only from South Tyrol, but it is probably more widespread in the Alps.
Growth form: Crustose
Substrata: soil, terricolous mosses, and plant debris