Marcetia wilburiana is described and illustrated from the southwestern region of the Chapada Diamantina in Bahia, Brazil, where it appears to be a rare and local species of campo rupestre. Its affinities appear to be with M. ericoides and M. shepherdii, both of which have a wiry subshrubby habit; small, coriaceous, glabrous leaves that are appressed and imbricate on uppermost cauline internodes; and solitary flowers. It differs from both species in having abaxial foliar surfaces that are longitudinally grooved between the callose-thickened margins and midvein, calyx lobes and hypanthia that are moderately to copiously beset with spreading gland-tipped trichomes 0.5–1.0 mm long, and petals that terminate in a persistent glandular trichome. The new species and presumed relatives are mapped and a key is provided to species in the informal ericoid group.