Roccella albida

Roccella albida has a distinctively shaped thallus, which forms branches that are terete (cylindrical and smooth) or slightly foveate (marked with small depressions). These branches generally range in length from 5 to 20 cm and have a colouration that varies from white to white-greyish. Soredia, which are reproductive structures for asexual reproduction, are infrequently found in this species and show a negative reaction to the C spot test.^[2]

The medulla, the inner tissue of the thallus, is byssoid or nearly byssoid, meaning it has a fibrous or cottony texture. Its colouration is predominantly white, though it can sometimes appear pale yellowish-brown, especially in the lower parts of the lichen. Ascomata, the spore-producing structures, are a common feature in Roccella albida. They often appear sessile (directly attached without a stalk) and have strongly undulating margins, which give them a knotty appearance. The ascospores of Roccella albida measure between 22 and 26 μm in length and 5 to 6 μm in width, with an average size of approximately 23.8 by 5.5 μm.^[2]

Chemical spot tests yield negative results for the medulla with both potassium hydroxide (K) and calcium hypochlorite (C), indicated as K− and C−, respectively. However, the cortex is C+ (red), and K−. The disc of the ascomata is C−. In terms of its chemical makeup, Roccella albida contains secondary metabolites (lichen products) such as erythrin, lecanoric acid, and protocetraric acid, as identified by high-performance thin-layer chromatography.^[2]

Roccella albida is native exclusively to the Galápagos Islands, with its presence confirmed on the islands Santa Fe, Floreana, Pinzón, Rábida, San Cristóbal, Santa Cruz, and Española.^[3] This species thrives in coastal areas, predominantly on vertical rocks and cliffs.^[2]