The new genus Saxiloba is described with the two species S. firmula from the Caribbean and S. hawaiiensis from Hawaii. Saxiloba is characterized by a unique, placodioid thallus forming distinct lobes, growing on rock in shaded to exposed situations with a trentepohlioid photobiont and a fenestrate thallus anatomy with distinct surface lines. The material is often sterile, but Porina-like perithecia and ascospores had previously been described for the Caribbean taxon and were here confirmed for both species. Molecular sequence data also confirmed placement of this lineage in Porinaceae. Its position within that family supports the notion that Porinaceae should be subdivided into a larger number of genera than proposed in previous classification attempts. Compared to other Porinaceae, Saxiloba exhibits a unique morphology and anatomy that recalls taxa in the related family Graphidaceae and it substantially expands the known phenotypic variation within Porinaceae. The two recognized species are similar in overall morphology but, apart from their disjunct distribution and different substrate ecology, differ in lobe configuration, color and disposition of the crystal clusters and resulting surface patterns.