The crustose lichen biota of coastal rocks in South Brazil was investigated. Several distinct lichen zones were found: a littoral black zone, a supralittoral yellow zone and a grey zone with species restricted to either exposed granite, dry overhangs, damp overhangs or places subjected to run-off. Dendrographa austrosorediata is newly described, with a crustose, flat to partly curling up or blister-like thallus which is much dissected, whitish grey, 0·1–0·2 mm thick; surface minutely densely cracked, rimose, with cracks intersecting at each c. 0·1 mm; soredia whitish to bluish grey but asymmetrically blackened in the direction facing the light, originating on the thallus surface, in initially discrete convex soralia. The phylogenetic position of this new species was traced by molecular methods. Stigmidium marinum, generally regarded as a lichenicolous fungus, was found as a free-living lichen, thousands of kilometres away from the nearest known occurrence of any purported host.