SUMMARY
A formal taxonomic revision of tke neotropical grass genus MesosetumSteudel (Gramineae: Paniceae) is presented. Mesosetum can be distinguished from the other genera in the tribe by tke solitary, terminal spike, the first glume of the spikelet turned towards the rachis, and, the caryopsis with linear hilun. The morphological features that have proved most useful in distinguishing the species ate the presence or obsence of wings on rachis, and, the form, relative size, number of nerves and ornamentation (hairs and/ or awn) of glumes and lower lemma. Twenty five species are considered in Mexico, all Central America (expect El Salvador), Cuba, Jamaica, Trinidad, Guyana, French Guyana, Suriname, Venezuela, Colombia, Bolovia, Paraguay and Argentina. Detailed descriptions, complete synonymy, illustrations and a key to the species are given.