Pappophorum Schreb. is a genus of perennial grasses included in Chloridoideae, found in arid and semiarid grasslands of the Americas. The genus is monophyletic, a sister group to Tridens Roem. & Schult., and the clade formed by these two is sister to Neesiochloa Pilg. Some taxonomic treatments in Pappophorum have repositioned taxa and indicated synonymizations based on morphological attributes. One of the classic examples of delimitation proposals in the genus concerns the morphological boundaries between P. subbulbosum and P. mucronulatum in the Southern Hemisphere, as well as between P. vaginatum in the Northern Hemisphere. This complex species serves as a valuable biological model, demonstrating that comparing delimitation proposals with phenotypic data can be sufficient for discussing and clarifying taxonomic issues. In this study, we tested species circumscription proposals as taxonomic hypotheses using a statistical framework that assesses the possibility of classifying all variation in the samples as a single species. This statistical routine integrates univariate, multivariate, simple Bayesian classification, and morphological classification models to answer: (i) what is the diagnostic potential of morphological characters between taxa; (ii) which classification proposal better accommodates the morphological variation of the species; and (iii) what level of morphological overlap can exist in recently diverged groups. The MCluster analysis indicated that the unsupervised classification of three species was the best taxonomic model. Six characters were statistically significant for distinguishing at least one species in the complex. Our results indicate that P. subbulbosum should be recognized as an accepted species, warranting its reinstatement and suggesting complementary descriptions for P. mucronulatum and P. vaginatum.