A revision of Monimiaceae from the Southern limit of the Atlantic forest domain resulted in the discovery of a species heretofore undescribed. Mollinedia leucantha, a treelet endemic to the Atlantic coastal moist forest in southern Brazil, is described and illustrated. Morphologically the new species is most similar to Mollinedia schottiana, from which it is set apart by characteristics in the rhytidome, leaves, trichomes, flowers and fruitlets, as well as by distinct flowering times. Additionally, scanning electron microscopy (SEM) images of the flowers and a key to distinguish morphologically similar or related species in the subtropical Atlantic forest are presented. A preliminary extinction risk assessment is also provided for the new species.