Aristida helleriana (Poaceae, Aristidoideae), una Nueva Especie Endémica del Pampa en Rio Grande do Sul, Brasil

Aristida helleriana M. Marchi, J. Mujica & R. L. Barbieri is a new species of Poaceae (Aristidoideae) collected at Sao Miguel's Farm, in Tapes, Rio Grande do Sul State (Brazil), during a floristic survey in an area where in situ conservation of Butia odorata (Barb. Rodr.) Noblick (Arecaceae) has been done. Aristida helleriana differs from A. laevis (Nees) Kunth, its closely related species in the study area, due to its few-flowered panicle, with branches bearing spikelets arranged helically and discontinuously along the rachis, leaving it fully exposed in some sections. The new species is distinguished by its lower lemmas 1–3 mm (vs. 8.5–13 mm in A. laevis) and shorter awns 11–17(19) mm (25–50 mm in A. laevis).