A new species is described, Polymeridium stromatocorticatum B.Barbosa, Aptroot, L.A.Santos & M.Cáceres, sp. nov. found in the Caatinga Biome, collected at Raso da Catarina Ecological Station (Bahia, Brazil). The new species is characterized by the combination of a corticated thallus and aggregated ascomata, while the ascospores exhibit the typical characteristics of a Polymeridium (Müll.Arg.) R.C.Harris. The genus has its greatest absolute world diversity in this region of NE Brazil, especially in areas of the Caatinga. Most of the species found in this region express peculiar characteristics related to the chemistry of the thallus, due to the presence of lichexanthone and the lack of inspersion of hamathecium. In addition, an updated checklist of Brazilian species is provided.