Rhabdodendraceae is recorded for the first time in the vascular flora of Colombia and the upper Río Negro basin, based on collections of Rhabdodendron amazonicum from the upper Cuyarí river, Guianía department, Colombia, and the upper Isana (Içana) river, Amazonas state, Brazil, respectively. These two localities extend considerably the northwesternly distribution of this taxon inside the Amazon Basin. Notes about the phytogeography (e.g. insights as to why this species has not yet been found between Manaus and the confluence of the Guainía and Casiquiare rivers), the habitats of R. amazonicum, and an updated overview of the known specimens using a geographic distribution map of this taxon is also included. The discovery of this family in the upper Río Negro region, demonstrates the value of field work through alliances between private initiatives and the Kuripaco nation.