Januaria is described as a new monospecific genus of Rubiaceae, based on material from Januaria, northern Minas Gerais, Brazil. The new taxon is endemic to Brazil, occurring in a vegetation type that is known locally as ``carrasco'', in the southern limit of the Caatinga biome. Morphological (including palynological and SEM analyses) and molecular phylogenetic analyses based on nuclear (ETS, ITS) and plastid (atpB- rbcL, petD, rps16, trnL-trnF) sequence data were performed in the Spermacoce clade (tribe Spermacoceae). The molecular position and morphological features (a unique fruit dehiscence type, and pollen exine with simple reticulum) support Januaria as a new genus, with Mitracarpus as sister group, from which it differs principally in calyx morphology, corolla shape, and fruit dehiscence. Additionally, a further comparison with other morphologically similar genera is presented. We provide a formal description of Januaria, together with a distribution map and comments on its conservation. In addition, a discussion about the Brazilian endemics of the Spermacoce clade is given, also with a key to all the genera of this group present in the country.