A first comprehensive taxonomic study was conducted on saxicolous and corticolous species of the lichen genus Porina (Porinaceae) in Japan, and twenty species were recognized. Three new species are described: Porina flavonigra, P. tosaensis and P. yoshimurae. Four species are reported as new for Japan: P. exserta, P. orientalis, P. papuensis and P. ulceratula. The term ''thalloid exdpleMis proposed for the thallus or thallus-like covering over the proper exciple. A key to the species, and illustrations and descriptions in detail for each of the seven species based on the Japanese materials are provided.