A new species of Acanthothecis is described in the Atlantic Forest of northeastern Brazil. Unlike any other species in the genus, it has distinctly pseudo-stromatic ascomata that resemble those of the genus Sarcographa. However, its apically spinulose paraphyses, I-negative ascospores with thin endospore closely resemble those of other Acanthothecis species. A previous molecular phylogenetic analysis places the new species close to the type species of Acanthothecis, A. hololeucoides. The discovery of this unique new species underscores the importance of thorough biotic surveys in the Atlantic Forest of Brazil, where it is likely that many more unknown lichen species await discovery.
