Three new species of the Neotropical genus Marcetia are described and illustrated: Marcetia barbadensis, Marcetia minima, and Marcetia serratifolia. The three species are known from small isolated populations in mountains of the Chapada Diamantina, Bahia, Brazil. The recognition of Marcetia barbadensis and Marcetia serratifolia is confirmed with an updated molecular phylogeny of the tribe Marcetieae (based on ETS, ITS, accD-psaI, atpF-atpH, trnS-trnG, psbK-psbL, ndhF and rbcL), and by morphological and morphometric studies. In turn, the recognition of Marcetia minima, a new species known only from the type gathering collected about 30 yr ago, is based on analyses of leaf and anther connective shape, as well as linear measurements of vegetative and reproductive structures. Based on the new phylogenetic hypothesis for Marcetieae, we reconstructed the evolution of habit and petal color in the tribe, and showed that prostrate plants and white flowers evolved repeatedly from ancestors with an erect habit and pink to magenta petals. We also provide notes on the intergeneric relationships and phylogeny of Marcetia and evaluate the generic placement of the recently described Acisanthera saxatilis.