Species and series boundaries of Solanum series Longipedicellata (Solanaceae) and phenetically similar species in ser. Demissa and ser. Tuberosa:: implications for a practical taxonomy of Section Petota

Species boundaries were assessed by phenetic analyses of morphological data for all species of wild potatoes (Solanum section Petota) assigned to ser. Longipedicellata: S. fendleri, S. hjertingii, S. matehualae, S. papita, S. polytrichon, and S. stoloniferum. These six tetraploid species grow in the southeastern United States (S. fendleri) and Mexico (all six species). We also analyzed morphologically similar species in ser. Demissa (S. demissum) and ser. Tuberosa (S. avilesii, S. gourlayi, S, verrucosum). We chose S. verrucosum and S. demissum as Mexican representatives, and S. avilesii and S. gourlayi as South American representatives of other series that are difficult to distinguish from ser. Longipedicellata. We also analyzed morphologically more dissimilar species in ser. Tuberosa (S. berthaultii) and ser. Yungasensia (S. chacoense). The results support only three species in ser. Longipedicellata: (1) S. polytrichon, (2) S. hjertingii + S. matehualae, (3) S. fendleri + S. papita + S. stoloniferum. Solanum avilesii, S. gourlayi, and to a lesser extent S. demissum and S. verrucosum are very similar to members of ser. Longipedicellata and are difficult to distinguish practically from them, despite differences in chromosome numbers and crossability relationships. These data help document and explain the extensive taxonomic difficulty in sect. Petota, highlight conflicts between biological and morphological species concepts, and add to a growing body of evidence that too many wild potato species are recognized.