Chloroplast DNA restriction analysis has been used to test the series classifications of the Mexican and Central American representatives of Solanum sect. Petota of Rydberg, Bukasov, Hawkes, and Correll. Three clades are supported: 1. all species in series Morelliformia, Pinnatisecta, and Polyadenia exclusive of S. bulbocastanum and S. cardiophyllum. Subclades within clade 1 include S. trifidum and S. tarnii; S. x michoacanum and S. pinnatisectum; S. brachistotrichum and S. stenophyllidium; S. clarum and S. morelliforme; and series Polyadenia; 2. S. bulbocastanum and S. cardiophyllum; 3. S. verrucosum (a Mexican diploid), the Mexican polyploid species, and the South American species. Within clade 3, series Conicibaccata forms a well-defined subclade, whereas S. verrucosum, series Longipediceltata, series Demissa, and the South American species form another. In reference to the latest classification of Hawkes, series Conicibaccata and Polyadenia are supported as monophyletic; the Mexican diploids are paraphyletic; and series Demissa, Longipedicellata, and S. verrucosum (series Tuberosa) form one monophyletic assemblage. Species within series Longipedicellata and Demissa are polyploid, possibly of hybrid origin, and may need less conservative markers or biparentally-inherited probes to distinguish them. These molecular results are compared to the diverse data sets that have led to this classification.
