Thallus effuse, to 5 cm across, areolate, composed of thin, angular, flat to slightly convex, pale grey areoles, 0.20.3 mm across; medulla I. Primary photobiont chlorococcoid; cells 59 µm diam. Secondary photobiont comprised of numerous small (up to 0.25 mm across) clumps of cyanobacteria scattered over the surface, cells of two types; short, branched, yellow-brown filaments, 1520 µm across, 12 cells wide (Stigonema), plus groups of 24 cells in a reddish (K+ purple) sheath, cells 5 µm diam. (Gloeocapsa).
Apothecia frequent, adnate to sessile, black, flat to convex, lecideine, 1.01.5 mm diam., ħ orbicular but often confluent and then angular; proper margin rarely discernible, even in young apothecia. Hymenium 5065 µm, streaked with red-brown pigment (K+ olivaceous-brown); paraphyses rather sparse and inconspicuous, simple, 1.01.5 µm thick, apices not pigmented or capitate. Asci cylindrical to somewhat clavate, 4045 × 1215 µm, tholus I+ pale blue with a darker axial tube (?Porpidia-type); ascospores hyaline, (0)1-septate, 1012 × 3.54.0 µm. Hypothecium massively developed and carbonaceous, dark red-brown (K+ olivaceous-brown), internal structure not discernible.
Conidiomata: pycnidia, uncommon, black, 0.100.15 mm wide; ostiole gaping at maturity; wall in section dark red-brown (K+ olivaceous-brown); conidia bacilliform, 78 × 1 µm.
Chemistry: K, C, Pd. No substances detected by TLC.
Distribution and Ecology: Known from only three collections from mountainous sites on Campbell Island, New Zealand. Associated species are few but include Placopsis sp. (with a lichenicolous Cercidospora sp.) and Steinera radiata subsp. aucklandica P. James & Henssen.
Remarks: The new species is included in the recently described genus Bryobilimbia Fryday, Printzen & S. Ekman (Fryday et al. 2014.) because of its similarity to B. australis (Kantvilas & Messuti) Fryday, Printzen & S. Ekman (syn. Mycobilimbia australis Kantvilas & Messuti), which grouped with the type species, B. hypnorum (Lib.) Fryday, Printzen & S. Ekman, in that study. The bacilliform conidia are also consistent with a placement in Bryobilimbia. It is separated from B. australis, and all other species of the genus, by a combination of its saxicolous habit and consistently 1-septate ascospores.