Prunus grayana (subg. Padus) was found to serve as the uredinial-telial host of two distinct Tranzschelia species in Japan. Tranzschelia pruni-spinosae has been known to occur on P. grayana, and the other species was previously overlooked. The latter fungus was experimentally proven to form its spermogonial and aecial stages on Hepatica nobilis var. japonica f. variegata and f. magna. The fungus was similar in morphology and host relationships to Tranzschelia arthurii, whose spermogonial and aecial stages occur on H. nobilis var. acuta and uredinial and telial stages on Prunus serotina and Prunus virginiana (subg. Padus) and Prunus americana (subg. Prunophora) in North America. However, the spores at all stages in the life cycle of the Japanese fungus were significantly smaller than those of the North American fungus. Because of this, a new species, Tranzschelia asiatica, was proposed for the geographically separated fungus. This species is expected to occur in East Asia outside of Japan, but this is not yet confirmed. Key words: rust fungus, Uredinales, Rosaceae, Prunus, Ranunculaceae, Hepatica.