Calycacanthus is treated as comprising two species, C. magusianus and a newly described species, C. insularis. The genus is endemic to New Guinea and several adjacent islands. Calycacanthus magnusianus is widespread in Papua New Guinea, whereas C. insularis is only known from several islands of that country in the southern Solomon Sea. The two species are similar in corolla size, shape, and coloration, but differ in calyx coloration, anther size, and pollen morphology. Both species are described (macromorphology and pollen), their distributions are mapped, habitats and phenological data are summarized, and preliminary conservation assessments are discussed.