Fimbristylis comprises about 300 species with pantropical and subtropical distributions, whose diversity is still being discovered. This study presents and describes three new species, Fimbristylis boldriniana, F. campestris and F. stipitata, and proposes lecto- and epitypification for Fimbristylis aspera from South America. In addition to complete morphological descriptions, we provide ecological information, geographic distribution, and conservation status for these species. This study provides the first identification key to all species of Fimbristylis that occur in Brazil.