Amandinea lobarica, a new corticolous lichen species, is described from high elevations in Guatemala. It is characterized by a thin, granulose, brownish thallus containing lobaric acid, small, convex lecideine apothecia, filiform conidia and large, narrowly ellipsoid ascospores with roughly ornamented walls. The new species is compared with other Buellia s. lat. taxa that possess rather large and strongly ornamented ascospores, such as Buellia hypothallina, here placed in synonymy with Gassicurtia vaccinii, Amandinea leucomela, A. mediospora, A. megaspora, A. subduplicata and five very closely related taxa treated here as belonging to the Amandinea incrustans group. Two tables summarizing the main differences between these species and a key are provided. New data on the chemistry of A. leucomela and a new record of A. montana for Guatemala are also included.