The alkaloids of two Amazonian species of Tabernaemontana (T. riedelii and T. rigida) were studied. From T. riedelii, the new alkaloids (+)-8-oxominovincine and (+)-minovincine, along with a mixture of (±)- and (+)-vincadifformine, were isolated; all have the aspidospermine-type skeleton. From T. rigida, (±)-vincamine, (+)-vincamine, (+)-apovincamine, and a mixture of (±)- and (-)-14-epivincamine were obtained, all with the eburnamine-type skeleton. Isolation involved solvent extraction, chromatography, and crystallization. Characterization was performed using UV, IR, NMR, mass spectrometry, elemental analysis, and comparison with authentic samples. Stereochemical assignments were made based on spectral data and known stereochemistry of related compounds. Chemotaxonomic implications are discussed: T. rigida's eburnamine-type alkaloids differ from most previously reported Tabernaemontana alkaloids (ibogamine-type), supporting re-evaluation of its botanical classification given its history of repeated reclassification.