The Cladia aggregata group of lichen-forming fungi comprises multiple species that are difficult to differentiate based on phenotypic characters. It has a wide distribution across several continents, but is most diverse in Australasia. We aimed to delimit the species complex further, investigate the relatedness of the lineages, and examine their distributional ranges and phenotypic traits. We used Restriction Site Associated DNA Sequencing (RAD-seq) to compare thousands of loci across 91 individuals from the Americas, Asia, and Australasia. All Asian samples formed a distinct, monophyletic clade in all phylogenetic trees, while the American samples divided into two clades, one comprising South American samples and another comprising Caribbean samples, with the latter representing C. aggregata sensu stricto, as the type specimen was collected in Jamaica. Further population-genomic analyses support the conclusion that the Asian samples are genetically distinct and are here described as a new species. The new species, Cladia asiatica, accommodates the Asian samples previously included in C. aggregata. Our analysis highlights the potential of next-generation sequencing to reveal hidden diversity and resolve the phylogeny of this species complex and lichen-forming fungi in general. Keywords: next-generation sequencing; systematics; phylogenetics; molecular variation; biogeography.