The genus Umbilicaria is represented by four species in the Hawaiian Islands. Three species formerly considered endemic are placed in synonymy with widely distributed Northern Hemisphere taxa. Thus, U. hawaiiensis is synonomous with U. decussata,while U. magnussonii and U. pacifica are synonymous with U. hirsuta. Two additional species, U. aprina and U. hyperborea, are also present. Hawaiian specimens are most common above 3500 m, all are sterile, and it is suggested that their presence in the Hawaiians Islands is the result of single colonization events.