Chloroplast DNA phylogenetics of the North American chestnuts and chinquapins (Castanea Mill., Fagaceae)

Evolutionary relationships and genetic structure of the North American Castanea were investigated using chloroplast DNA sequence data. Six plastome loci were PCR-amplified and sequenced in 77 accessions representing the three currently recognized North American Castanea species. Diagnostic morphological character states and a unique haplotype were shared among C. pumila and a plant tentatively identified as C. dentata in one sympatric site, suggesting past hybridization and chloroplast capture. Surprisingly, the cpDNA phylogeny did not agree with previous taxonomic treatments. The inability to distinguish between deep coalescence and interspecific hybridization as the causes of haplotype sharing makes phylogenetic reconstruction of the North American Castanea species difficult. Although non-D haplotypes were previously reported as diagnostic for C. pumila and hybrids, multiple non-D haplotype C. dentata were documented in the Southern Appalachians and Piedmont. The diversity of haplotypes observed in southern C. dentata populations provides further impetus to conserve C. dentata in the Southeast