Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Eriosema grearii, a new species for the genus (Leguminosae, Papilionoideae, Phaseoleae, Cajaninae), is described and illustrated. Similar to E. heterophyllum, it differs from it morphologically by the free (vs. joined) stipules, lax flowers distributed along the inflorescence axis (vs. congested and concentrated at its apex), inflorescences not opposite to the leaves (vs. opposite), and leaflets with secretory cells at the base of trichomes (vs. absence of secretory cells at the base of trichomes). A survey of the leaflet secretory structures revealed that E. grearii has distinct secretory structures, referred here as secretory- base trichomes, and reported for the first time for the Phaseoleae tribe. An identification key for the Eriosema species in Mato Grosso do Sul, where the new species occurs, is provided.2632122130CNPq [457911/2013-1, 140598/2015-4, 302657/2011-8]CAPESFAPESP [2015/13386-0]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)