Thallus: crustose, bullate and, especially when epilithic often forming small cushions, effuse, smooth to slightly verrucose, 0.3-0.7 mm diam. surface: grayish white, often with slightly brownish parts; soralia not seen cortex: 20-40 µm thick medulla: white, chalky Ascomata: sometimes nearly stromatoid, numerous, circular in outline, sessile or subimmersed with base not constricted, 0.5-3 mm diam.; exciple: entire or slightly undulating, in level with or only slightly protruding above the disc; epithecium: light brown to brown, 25-60 thick; hymenium: hyaline asci: clavate, 70-110 µm, 8-spored ascospores: fusiform, curved, smooth, 3-septate, hyaline, 25-31 x 4-5 µm Spot tests: thallus K-, C-, KC-, P- Secondary metabolites: roccellic acid. Substrate and ecology: most common on bark and wood of various trees and shrubs near the sea, but is also found on rocks World and Sonoran distribution: found only in California from San Francisco in the north down to San Diego and farther south in Baja California to Rosario de Arriba. Notes: Roccellina franciscana is distinguished from Roccellina conformis by its white-grayish thallus with K- and P- reactions and the apothecia which are much more undulating or nearly stromatoid and are often subimmersed and without a constricted base.