Siphocampylus flavescens is a new species endemic from the Serra Negra region, in the Serra da Mantiqueira complex, in Minas Gerais state, Brazil. It is characterized mainly by being a polycarpic decumbent subshrub, with whorled phyllotaxis (usually three leaves per node), and by its entirely yellow corolla, which differentiates S. flavescens from all other Brazilian species of Siphocampylus. Morphologically, it is more related to S. fluminensis, from which it can be distinguished mainly by the entirely yellow corolla (vs. bicolor, with the tube reddish and the lobes yellowish or greenish). Minor differences include the equally denticulate leaf margin, with reduced teeth, the reduced widely obconic hypanthium, and the rounded capsule of S. flavescens (unequally denticulate to fimbriate leaf margin, larger obconic hypanthium, and obconic capsules in S. fluminensis). The new taxon is here described. We provide a distribution map, photographs, and an identification key to the Siphocampylus species found in Minas Gerais state. We also informally propose the inclusion of S. flavescens in the IUCN Red List as an Endangered (EN) species due its small area of occurrence and the growing human impact in the region.