A monograph is presented of Hypenia in the plant family Labiatae. Hypenia was formerly a genus but in this study it is treated as 23 species in six sections of the genus Eriope. 22 of the 23 species treated in this study occupy relatively restricted ranges in the savannas of the central Brazilian plateau and neighbouring parts of the Serra do Espinaco in eastern Brazil. The remaining species occurs in dry scrubland in north-eastern Brazil with a disjunction to savanna in northern Venezuela. The previous classification and taxonomic history of Hypenia are outlined followed by a discussion of morphology and cytology in the group. Observations were made on pollination biology of selected species. Cladistic investigations were conducted using morphological characters and the ITS region of the nuclear genome. The morphological and molecular analyses were then combined in a single analysis. The cladistic analyses indicated that Hypenia was a paraphyletic genus and that generic boundaries between Hypenia and Eriope needed to be reconsidered. The classification of Hypenia was revised in the context of the phylogeny generated by the combined analysis and with consideration given to the theory of classification with particular reference to recent literature on the subject. The largest number of species in Hypenia belonged to the 'macrantha complex', a group of red-flowered species endemic to central Brazil. Considerable revision of the species in this group was required. The 'macrantha complex' was recognised as Eriope section Hypenia with two subsections. One of the subsections was characterised by resupination of the corolla, a previously overlooked character. Five new species of Hypenia are presented in this account. Distribution maps of all the species described were followed by a discussion of biogeographic patterns in the group.