Galapagos Species Database

Thallus main branches terete, secondary branches occasionally partially compressed but not distinctly flattened, smooth or foveate, usually 5–20 cm long, grey to brownish-grey; soredia present (rarely absent), C–; medulla compact, pale ochre to ochre or in lower branches often brownish to dark brown. Ascomata usually absent, rarely present, circular in outline slightly undulating margin, sessile with constricted base; ascospores 21–30 × 5–7 μm (average = 24.3 × 6.1 μm). Spot tests: medulla K–, C–; cortex K–, C+ usually distinctly red; disc faintly C+ red. Secondary metabolites erythrin, protocetraric acid.

Roccella margaritifera is characterized by its sorediate C+ red thallus as compared to the morphologically identical and sympatric species R. nigerrima, which has a C– thallus reaction. Spot testing is the only macroscopic way to distinguish between the two. Roccella lirellina from Peru, is also extremely similar and morphologically more or less identical to both R. margaritifera and R. nigerrima (see above). R. margaritifera has been found fertile at only one location.