Morphological distinctions were evaluated between taxa of Panicum section Virgata Nees as recognized by Hitchcock and Chase (1951) and Freckmann and Lelong (2002b): P. virgatum var. virgatum, P. virgatum var. cubense, P. amarum subsp. amarum, and P. amarum subsp. amarulum, using morphometrics and greenhouse experiments on material from the southeastern United States, a region with the most extreme overlap in distribution. 31 characters for 104 specimens were subject to univariate, bivariate, and multivariate analyses. Spikelet bivariate graphs showed two groups with large (C) and small (A+B) spikelets. When habitat, distribution, and phenology was superposed on these graphs, non-exclusive trends polarized the small spikelet group into two groups (A) and (B). Morphogroups A, B, and C did not overlap on PCA graphs, but were not separated by gaps. Results show two morphogroups present: A+B (P. virgatum var. virgatum, var. cubense, P. amarum subsp. amarulum) and C (P. amarum subsp. amarum)
