Thallus: fruticose, erect or pendent, both main and terminal branches terete, 5-10 cm long lobe surface: white grayish, smooth medulla: white but brown in the holdfast zone, usually with a yellowish tinge Ascomata: usually present, circular in outline with slightly undulating margin, sessile with constricted base, up to 2 mm diam.; hymenium: 70-90 µm; paraphysoids: sparsely branched, hyaline, <2 µm diam. asci: clavate, 60-85 x 12-14 µm, 8-spored ascospores: fusiform, curved, hyaline, 3-septate, 23-27 x 5-6 µm; walls: smooth Spot tests: cortex K-, C-, KC-, P-; medulla K-, C-, KC-, P- Secondary metabolites: not investigated. Substrate and ecology: on rocks near the sea World distribution: South America, from central Chile to the Galapagos Islands, and northwards to Baja California Sonoran distribution: only known on cliffs near Todos Santos in southern Baja California Sur. Notes: Roccella portentosa is distinguished from R. decipiens and R. peruensis mainly by its terete and smooth branches and its C- thallus reaction. No representative from the R. portentosa complex has been described from the Sonoran region. The specimens collected from Baja California have clearly sessile apothecia and the thallus cortex and medulla are C-. South American specimens have apothecia which are usually more or less immersed and their thallus C reaction is variable ranging from fully C+ or, C- cortex but C+ medulla, or rarely completely C-. In South America sorediate specimens may also be involved in species pair complexes. The identification of the Baja Californian specimens as R. portentosa should be considered as provisional until the genus Roccella has been revised.