Mesosetum (Poaceae, Arthropogoninae) is a Neotropical genus with its greatest diversity in Brazil, which has 22 of the 25 recognized species, 14 of which are endemic to this country. One more endemic species, Mesosetum filgueirasii, here described, is allied to M. penicillatum because it has the lower lemma covered by an indumentum in tufts. This work establishes the distinction between these species and provides the anatomical description of the leaf blade of M. filgueirasii. The new species is known only from the area called “Garganta,” located on the border of the Brazilian states of Tocantins and Bahia. It grows in Cerrado vegetation, in eroded soil. This is the first report of anatomical data supporting taxonomic studies in this genus.