Ab omnibus speciebus generis Rimulariae habito bryicola, thallo brunneo granulato et lichenalibus substantilis absentis differt.
Typus: Falkland Islands, East Falkland, Mt. Usborne, Table Rock, UTM 21F UC 7868 [51°719500’S, 58°766000’W], 1800 ft. [549 m], feldmark outcrops on summit, 9 January 1968, H. A. Imshaug (40082-B) & R. C. Harris (MSC-0108540—holotypus; BCRU— isotypus).
Thallus of ±dispersed brown, often grey pruinose, bullate areoles (0.13–)0.15–0.20 mm across; growing over Andreaea sp. Cortex not clearly defined but cortical cells brown, 5 mm across. Medulla I–. Photobiont chlorococcoid, cells 8–12(–15) mm.
Apothecia black, lecideine, orbicular, occasionally somewhat angular, flat 0.5–0.7 mm diam., proper margin thick (0.5 mm), raised and persistent. In section:proper excipule dark brown, cupular, 100 mm wide. Hymenium hyaline, I+ blue, 130–140 mm tall; epihymenium 10–15 mm thick, pale brownish; paraphysoids 1.0–1.5 mm thick, septate and moniliform, richly branched and anastomosing, apices swollen to 4 mm with dark cap. Asci c. 55–60 × 20–30 mm, broadly cylindrical to sub-clavate, Rimularia-type; ascospores hyaline, simple, 8 per ascus, 15–18(–21) × 10–12 mm, thick-walled (c. 1 mm thick). Hypothecium pale to mid brown merging into the exciple.
Conidiomata not seen.
Chemistry. C–, K–, KC–, Pd–. No substances detected by TLC, but material very scanty.