Distribution: N - Frl (TSB 25120), Ven (Nascimbene 2004), Lomb, Piem (TSB 34466).
Description: Thallus foliose-umbilicate, attached by a central holdfast, usually monophyllus, 0.6-5 cm broad, smooth or slightly rippled, grey to (rarely) grey-brown, pruinose or epruinose, 0.4-0.7 mm thick and greenish when wet, growing amphibious in cold freshwaters; lower surface bright red-brown to yellowish, smooth to ridged but not veined, erhizinate. Medulla white, I+ red. Upper and lower cortex c. the same thickness, of paraplectenchymatous cells. Perithecia numerous, immersed in the thallus and scattered over almost the whole upper surface (appearing as black dots), in section pale, with only the tips brownish, c. 0.2-0.4 µm in diam. Hamathecium or periphyses and periphysoids, interascal filaments absent; hymenial gel hemiamyloid. Asci 8-spored, clavate, fissitunicate, the wall thickened above, not amyloid. Ascospores 1-celled, hyaline, elongate-elliptical (9-)13-17 x 4-7 µm. Pycnidia rare, black, immersed. Conidia bacilliform, 4-5 µm long. Photobiont chlorococcoid. Spot tests: all negative. Chemistry: without lichen substances.
Note: a rather poorly understood, but characteristic, perhaps holarctic species found on calciferous or base-rich siliceous rocks in periodically wet places, or near the ground in upland areas.