Thallus pale grey, composed of thick convex areoles (0.3–0.5 mm) usually in small (to 1 cm diam) patches, but effuse and with thinner thallus with a black fimbriate prothallus when growing on quartzite. Cortex not clearly defined but with a thin (3 µm) pale brown layer immediately above the photobiont layer and a hyaline epinecral layer (10–50 µm) that is I+ violet. Medulla inspersed with numerous fine granules (not dissolving in K or N), I+ violet. Photobiont chlorococcoid, cells 8–12(–15) µm.
Apothecia black, lecideine, rounded to angular, occasionally lirellate with slit-like disc, flat 0.4–0.6 mm diam., proper exciple thick (0.5 mm), raised and persistent. Thecium hyaline, I+ blue, 80–100µm tall; epihymenium 10–15 µm thick, brownish-grey (K+ purple-brown; Sedifolia-grey); paraphysoids 1.5– 2.0 µm thick, septate and moniliform, richly branched and anastomosing, apices swollen to 5 µm with dark cap. Asci c. 50 × 15–20 µm, broadly sylindrical to sub-clavate, Rimularia-type; ascospores hyaline, simple, 8/ascus, (13–15 × 9–10 µm, thick-walled (c. 1 µm thick). Hypothecium hyaline above (subhymenium) of randomly arranged swollen hyphae, pale- to mid-brown merging into the exciple. Excipulum dark brown, cupular, 50–70 µm wide, of dark-walled, elongated cells 10–15 × 3–5 µm.
Conidiomata not seen.
Chemistry: C–, K–, KC–, Pd–. No substances by TLC.
Microscopically similar to Rimularia psephota but with a white, discrete thallus lacking norstictic acid.
Known only from the Falkland Islands and Isla de los Estados.