The Phylogeography of North American Chestnuts and Chinquapins (Castanea Mill., Fagaceae)
Faculty Chair: Dr. Hill Craddock
North American Castanea Mill. (Fagaceae) consists of three morphologically variable species: Castanea dentata, Castanea pumila and Castanea ozarkensis. Taxonomy of these species has been complicated by intermediate morphology, similarity in growth habit, and putative naturally occurring hybridization where species' ranges overlap in the southeast. The main goals of the present study were to: 1) determine if genetics reflect the morphological variation observed in southeastern populations of North American Castanea, 2) explore the extent of cpDNA haplotype sharing among these taxa, and 3) map haplotype distribution in relation to morphotaxa. Finally, I wanted to use the information obtained from these analyses to gain insight into southeastern populations, where intermediate morphologies and putative hybridization are confounding taxonomy. I sequenced the trnV-ndhC intergenic spacer region (-380 bp) of the chloroplast for 233 Castanea accessions collected throughout the range of the genus, with a focus on southern Appalachian populations from Georgia, Tennessee and North Carolina. I identified four main chloroplast haplotypes and found that for three of these haplotypes. leaf morphology is a reliable indicator of haplotype identity. I found that the fourth haplotype is shared among accessions of C. dentata and C. pumila, and is also found in trees with intermediate morphology. The geographic mapping of these haplotypes revealed that each haplotype is found in a separate geographic range, allowing for the comparison of current distributions with locations of possible glacial refugia. Although the precise genetic basis of the confounding morphology in southeastern populations of North American Castanea is still uncertain, an intricate biogeographical history combined with the tendency of taxa within this genus to share haplotypes in sympatric areas could explain much of the morphological complexity of Castanea.