Multivariate and univariate analyses based on morphological characters were carried out in order to understand the taxonomic status of Senna spiniflora and S. chacoënsis. Fifteen morphological characters from herbarium specimens were recorded and analyzed by the Kruskal-Wallis test and principal components analysis. The type specimens and all available herbarium material were examined for the taxonomic study. The results showed that the taxa differed only by the character of stem pubescence and this feature displayed high variability. In parallel, the principal components analysis demonstrated that no clearly separated groups were recognized. Based upon these results, the synonymy of S. chacoënsis to S. spiniflora is proposed.