A revision of the native and introduced South American species of Brachiaria (Trin.) Griseb. and Urochloa P. Beauv. (Poaceae: Panicoideae: Paniceae).
The generic limits of Brachiaria and Urochloa are discussed. Brachiaria is represented in South America by the introduced species, Brachiaria eruciformis. The genus is characterized by dorsiventral inflorescences, spikelets with an upper anthecium that is early shedding, mucilaginous and smooth, and with a subcircular callus at its base. Urochloa comprises 22 species in South America, 9 of them introduced. The genus is characterized by radiate or bilateral inflorescences, spikelets with the upper anthecium that is not early shedding, is transversely rugose, aristulate or crested at the apex of the lemma, and has a triangular callus at its base. Both genera have Kranz anatomy. Eleven new combinations are proposed: U. albicoma, U. arrecta, U. humidicola, U. lorentziana, U. megastachya, U. mollis, U. multiculma, U. oblita, U. paucispicata, U. ruziziensis, U. vittata. The species are described, several of them illustrated and keys to all species are given; two new chromosome counts are included for U. lorentziana and U. paucispicata. Relationships of Brachiaria and Urochloa with related genera of the Paniceae are also included.