Apetahia and Sclerotheca are two small genera of Campanulaceae (subfam. Lobelioideae) endemic to South East Polynesia (French Polynesia and the Cook Islands).These groups comprise from small shrubs to small trees (up to 3 m tall) that are restricted to upland tropical rainforests and montane cloud forests, where they are generally found between 400 and 2000 m above sea level. We investigated their molecular phylogenetics by sequencing four plastid loci. We found that the two genera together form a well-supported Glade but did not find support for their reciprocal monophyly. The genus Sclerotheca is supported as monophyletic Glade that may be nested within a paraphyletic Apetahia. Because of their morphological similarities, we opted to treat them as a single genus, Scierotheca s.l., comprising ten species, and here provide the necessary new combinations, Sclerotheca raiateensis comb. nov. and Sclerotheca seigelii comb. nov. The expanded genus Sclerotheca has a patchy geographical distribution with remarkable disjunctions and may be undergoing a long-term decline. Conservation efforts to protect these highly threatened endemic species (all classified CR or EN according to the IUCN red List) are urgently needed, as they may be also considered as indicators of long-term ecological changes.