Through the study of the original description, types, herbarium material, fieldwork and molecular evidence, Loasa acaulis is reinstated, lectotypified and transferred to Grausa. Loasa acaulis was previously synonymized under Loasa lateritia. We now consider both as two different species for which a key and descriptions are herein provided. Key floral differences include size, shape, angle and colour of petals, shape of the nectar scales, and attachment position of the dorsal threads. We found no specimens that resembled intermediate floral morphologies. Scanning Electron Microscope studies of mature seeds show a strong affinity between the two species as they lack the outer periclinal walls and incomplete fenestration found in other members of Grausa. Additionally, the characteristic hilar cone of other species of Grausa, is always poorly developed in L. acaulis and G. lateritia. We sequenced five loci (four plastid and one nuclear) and inferred topologies with Maximum Likelihood and Bayesian approaches. Both plastid and nuclear phylogenies placed Loasa acaulis as sister to Grausa lateritia, and distantly related to Blumenbachia and Loasa. Finally, examination of herbarium specimens revealed that Loasa acaulis is not endemic to Chile as previously thought, but also found in adjacent Argentina.