Inga pitmanii K. G. Dexter & T. D. Penn., a new species of Inga Mill. from Madre de Dios, Peru, is described for the Fabaceae (Mimosoideae). Morphologically it is closest to I. chartacea Poepp. & Endl., with which it shares a broadly winged rhachis, spicate inflorescence, glabrous leaves, nine to 10 pairs of secondary veins, and similar calyx indumentum. Inga pitmanii differs from I. chartacea in the leaflet number (four pairs vs. usually two or three pairs), the foliar nectaries (cyathiform vs. patelliform), and the larger flowers (with corollas 9–11.5 mm vs. 4.5–7 mm). Phylogenetic analyses show this species belongs to a clade including I. acreana Harms and I. chartacea. This species was discovered during field surveys for an ecological study of the genus Inga at the Los Amigos Biological Station in Madre de Dios, Peru. These field surveys uncovered several potentially novel species of the genus Inga, none of which matched any known species based on vegetative characters and the majority of which are genetically distinct. Here we describe I. pitmanii as this is the only species that was collected in a fertile state. Given current and future limitations in taxonomic expertise and funding, we advocate consideration of nonconventional approaches to species discovery, such as combining biodiversity surveys with large-scale DNA sequencing. This would in turn allow ecologists, who often collect plants in poorly known regions, to make a greater contribution to the species-discovery process.