Dicorynia stands out among the 17 genera of the diverse legume subfamily Dialioideae as an example of extreme floral reduction and specialization. It has asymmetric flowers presenting a heteromorphic calyx, trimerous corolla, and pair of highly dimorphic stamens, with one or both anthers polysporangiate. The two species of Dicorynia are Amazonian trees, one of which is highly valued for its timber. Despite the economic importance of the genus and an abundance of new collections, no comprehensive taxonomic study of Dicorynia has been completed since the publication of Koeppen’s monograph almost six decades ago, in which two species were recognized, one of which divided into six varieties. The present work employs integrative analysis of geographical, ecological, and extensive specimen-based morphological data to test previous delimitations of species and varieties. A new classification is adopted in an updated and comprehensive taxonomic revision of Dicorynia. We maintain two morphologically distinct and geographically separated species, D. guianensis and D. paraensis. The former is restricted to portions of the Guiana Shield north of the Amazon basin. At the same time, the latter is broadly distributed in the Amazon basin, but mainly north of the Amazon River. We recognize several taxonomically significant entities within the latter species, which, because they display limited morphological overlap and substantial geographical sympatry, we treat as varieties. However, we reduce the number of varieties from six to four. The taxonomic treatment contains new descriptions and illustrations, distribution maps, including two new areas of occurrence, conservation status assessments for all treated taxa, and identification keys to distinguish them. Nomenclatural, biogeographical, and ecological comments, including two new lectotypifications, are provided.