Omphalodiella patagonica Henssen gen. et sp. nov. is described from two Patagonian localities in Argentina. In habit the new lichen resembles some species of Acarospora in having brown, peltate thalli less than 3 mm wide with immersed apothecia. The ontogeny and structure of the apothecia and pycnidia correspond, however, to genera of the Parmeliaceae. The apothecia are provided with a meristematic, cupular exciple, and the amyloid asci contain 8 or less, ± globose spores. The short-celled conidiophores produce rod-shaped conidia of bayonet type. The thallus is provided with a narrow paraplectenchymatic upper and a broad prosoplectenchymatic, strongly gelatinized lower cortex. The thallus contains gyrophoric acid; the cortex contains ‘glomellifera brown ’.