Abstract
Polyploidy, whole genome duplication, plays a major role in the evolution of angiosperms with multiple paleopolyploid events having been suggested making it plausible that all angiosperms have a polyploid event in their history. There are two types of polyploidy, autopolyploidy genome duplication within a species and allopolyploidy, whole genome duplication coupled with hybridization. Penstemon subsection Saccanthera is a species complex of closely related diploids and polyploids. The species in this complex are P. heterophyllus (2x, 4x), P. parvulus (4x), P. neotericus (8x), P. laetus (2x) and P. azureus (6x). Previous studies have hypothesized that P. azureus is an allopolyploid of P. parvulus (4x) X P. laetus (2x). To test the hypothesis of allopolyploidy in the origin of P. azureus and to determine possible progenitors two nuclear loci (Adh & NIA) and three chloroplast spacer regions (trnD-trnT, rpoB-trnC, rpl32-trnL) were sequenced from P. azureus, P. heterophyllus, P. laetus, P. parvulus, and P. neotericus. These data were analyzed in phylogenetic framework and network analysis was used on the nuclear data.The Adh and NIA datasets supported the allopolyploid origin of P. azureus with divergent Adh orthologs recovered in all five accessions P. azureus and divergent NIA orthologs recovered in three of the P. azureus accessions. Furthermore, the Adh and NIA datasets support three hypotheses for the possible progenitors of P. azureus: (1) P. heterophyllus (2x) X P. parvulus (2) P. heterophyllus X P. laetus and (3) P. heterophyllus (2x) X P. heterophyllus (4x). Markedly, all support P. heterophyllus (2x) as a progenitor. In addition, the Adh and NIA trees also suggest that P. neotericus is an allopolyploid, P. parvulus is an autopolyploid with two distinct origins and P. heterophyllus (4x) as an autopolyploid or allopolyploid. The cpDNA analysis resolved geographically structured clades. This pattern is best explained by local adaptation of the chloroplast genome and chloroplast capture. However, multiple origins of the polyploid species and gene flow could explain this pattern. In addition, the cpDNA tree and short branches in the Adh and NIA trees suggests that this species complex rapidly diversified in the Sierra Nevada Mountains. My study provides the first molecular phylogenetic evidence of the allopolyploid origin of P. azureus and has given insight into the origin of the other polyploids in this species complex. Furthermore, it has provided a foundation for further investigations of the diversification, speciation, and reticulation of subsection Saccanthera.