Mimosa cerifera , a new species from M. sect. Mimosa ser. Mimosa subser. Sparsae, is described and illustrated. This species is distinguished by a combination of characters, including the presence of a white-blue wax that covers all structures, fruits moniliform, non-planecompressed, glabrous, and articulated, and bracts persistent. Furthermore, Mimosa cerifera is only found in grasslands of the Pampa biome near Quevedos city in southern Brazil. We recommend that the species be evaluated as Critically Endangered according to the criteria B1 ab (i, iii, iv, v) + 2b (ii, iii); C2 a (ii).