Botanical Journal of the Linnean Society 158,1: 147-171 (September 2008).
Basionym: xxx.
Synonym: Index Fungorum
Type: St Helena. Prosperous Bay Plain, on track of access road north of Bone Gully, on basalt, altitude 330 m, 17.x.2006, A. Aptroot 66215 (holo. B; iso. ABL).
Thallus: Initially shrubby, becoming pendant with age, up to 20 cm in diameter but usually much smaller (c. 7 cm), without distinct holdfast, relatively sparingly antler-like branched, partly terete, but mostly flattened, never contorted, not canaliculate, never perforate, relatively slender, c. 0.51.2 mm wide, c. 0.20.5 mm thick, with at most few inconspicuous warts, greenish-grey, most parts with conspicuous whitish linear pseudocyphellae, the overall colour therefore pale grey. Branches generally linear, often bent below the apothecia (geniculate). Branch tips often minutely curved, usually not blackened. Thallus without soredia. Thallus section with conspicuous, rounded strands of cartilaginous tissue in the medulla and at the surface, which are mostly hyaline, but brownish in section near the surface. Photobiont in irregular groups throughout the medulla. Cortex indistinct. Apothecia common, c. 12 mm, rarely up to 3 mm in diameter, initially cupular but becoming distorted and somewhat convex when old, laminal, disc yellowish-grey, margin with white pseudocyphellae and in section with rounded strands of hyaline cartilaginous material like the thallus, ascospores straight to slightly curved, 1012 × 4.05.5 µm. Conidia not observed.
Photobiont:
Chemistry: Usnic acid with or without binonic and protocetraric acids (by TLC).
Ecology: It occurs on boulders and cliffs on the Prosperous Bay Plain and almost everywhere elsewhere on the island.
Molecular data: Genbank
Distribution: Database
Note: This species is characterized by its flattened, sparingly irregularly branched thallus with linear pseudocyphellae and laminal, solitary, large (c. 12 mm) apothecia. The thallus is markedly geniculate at an apothecium insertion. The thallus usually contains boninic and protocetraric acids. There is no close relative identified outside St Helena, but this species may be close to boninic acid-containing R. sanctae-helenae. The incorrect Leighton record of R. ceruchis (Ach.) DNot. (which is a South American endemic occurring along the Pacific coast only) may well have referred to this species.