Galapagos Species Database

Thallus main branches terete, secondary branches occasionally partially compressed but not distinctly flattened, smooth or foveate, usually 5–20 cm long, typically grey to brownish-grey; soredia present (rarely absent), C–; medulla compact, pale ochre to ochre or in lower branches often brownish to dark brown. Apothecia extremely rare, usually absent, circular in outline, with a slightly undulating margin, sessile with constricted base; ascospores not found. Spot tests: medulla K–, C–; cortex K–, C+ red; disc C reaction not possible to examine. Secondary metabolites galapagin, roccellin.

Roccella nigerrima is characterized by its sorediate, C– thallus as compared to the morphologically identical and sympatric species R. margaritifera, which has a C+ red thallus reaction. Spot testing is the best way to distinguish the two species. Roccella lirellina from Peru, is extremely similar and morphologically more or less identical to R. nigerrima, but R. lirellina is easily distinguished by its faintly C+ red thallus reaction. Roccella nigerrima has been found fertile only once, but then with a rudimentary ascoma.