This is the first floristic survey of grass species undertaken in Rio Grande do Norte. The family has great economic and ecological value. In the Seridó area, where the "caatinga vegetation" is open and shows a continuous herbaceous stratum, representatives of the family constitute the main component of the vegetation in the raining season. We documented the occurrence of 57 species of Poaceae, distributed in 34 genera, in the Seridó Ecological Station. Of those species, 41 are native to the area and 16 are exotic. The paper includes analytical keys for the grass tribes genera and species descriptions, a discussion about the delimitation of some species, the distribution of the species in the Station, and botanical illustrations. Eragrostis cilianensis (Bellardi) Vignolo ex Janch., Mesosetum annuum Swallen and Cenchrus ciliaris L. are recorded for the first time for the Flora of Rio Grande do Norte.
Caatinga; Gramineae; herbaceous plants
