Galapagos Species Database

Thallus branches terete, smooth or slightly foveate; usually 5–20 cm long; white to white-greyish; soredia rare, C–; medulla byssoid or nearly byssoid, white or sometimes pale yellowish-brown in lower parts. Ascomata common often sessile with strongly undulating margin giving it a knotty appearance (Fig. 5B); ascospores 22–26 × 5–6 μm (average = 23.8 × 5.5 μm). Spot tests: medulla K–, C–; cortex K–, C+ red; disc C–. Secondary metabolites erythrin, lecanoric acid and protocetraric acid.

Roccella albida is habitually similar to the sympatric species R. galapagoensis. It is distinguished from the latter species by its smaller size, the smaller growth and the whitish thallus colour and whitish medulla. Roccella albida is more rarely collected than the common R. galapagoensis. Sorediate individuals of R. albida may be confusingly similar to R. margaritifera but differ from the latter species by their smaller, more delicate thallus in combination with a whiter medulla composed of more loosely interwoven hyphae.