Botanical Journal of the Linnean Society 158, 1: 147-171 (2008).
Synonym: Index Fungorum
Type: St Helena, South of Gregory's Battery, on basalt, altitude 300 m, 19 October 2006, A. Aptroot 66677 (B - holotype, ABL - isotype).
Thallus: Initially shrubby, becoming pendant with age, up to 12 cm long but usually much smaller (c. 7 cm), without distinct holdfast, relatively sparingly antler-like branched, partly terete, but mostly flattened, often partly conspicuously corkscrew-like contorted, not canaliculate, sometimes perforate, papery thin, c. 0.34.0 mm wide, c. 0.20.3 mm thick, with at most a few inconspicuous warts, greenish-grey, most parts with numerous inconspicuous whitish linear pseudocyphellae that are confluent to fill most of the surface, the overall colour therefore pale grey.Branches in outline generally flabellate. Branch tips distinctly flabellate but generally divided into attenuating tips, sometimes minutely warted along the margins, usually not blackened, but often pinkish because of the decomposition of norstictic acid. Thallus without soredia, but tips in some specimens swollen and soredia-like abraded. Thallus section with conspicuous, rounded strands of cartilaginous tissue in the medulla and at the surface, which are mostly hyaline, but brownish in section when reaching the surface. Cortex indistinct. Apothecia unknown. Conidia unknown.
Photobiont: In irregular groups throughout the medulla.
Chemistry: Usnic acid, usually with (rarely without) norstictic and connorstictic acids (by TLC).
Ecology: On cliffs on the Prosperous Bay Plain and elsewhere on the island.
Molecular data: Genbank
Distribution: Database
Note: This species is characterized by a papery thin, flattened, flabellate but ultimately attenuating, often contorted, sparingly irregularly branched thallus without pseudocyphellae. The thallus usually contains norstictic acid. There is no close relative identified outside St Helena, but this species may be close to R. rigidella. This species is named in honour of the Dutch lichenologist and ecologist Rita Ketner-Oostra.