Systematics of the North American plums (Prunus subgenus Prunus section Prunocerasus; Rosaceae)

The North American plums (Prunus subgenus Prunus section Prunocerasus; Rosaceae) are a closely related group with approximately 17 commonly recognized species and lesser taxa. They are infamous for their very poor development of reproductively isolating barriers and most are interfertile in many combinations. This interfertility blurs nearly all morphologically-based taxonomic boundaries. The aim of this dissertation research was to infer a phylogeny for the group in an attempt to understand their complicated evolutionary history. Emphasis was placed on using molecular tools (e.g., PCR and DNA sequencing) to tease apart their intricate relationships. The importance of this course of study includes but is not limited to: (1) better understanding a difficult group of taxa for academic reasons, (2) accumulating data to better understand these taxa so that conservation efforts can be better focused (e.g., P. geniculata is Federally Endangered), (3) better understanding the relationships among a group of plants with economic importance, (4) testing the limits of tools currently used in plant molecular systematics---the North American plums posit a problem at the boundary between molecular phylogenetics and population genetics, and (5) adding to a body of knowledge surrounding longstanding biogeographic questions of North America.; The results of this course of study showed that (1) predictable rate heterogeneity exists among noncoding cpDNA regions and several rarely used regions provide more mutations to phylogenetic investigations than the most commonly used regions. (2) The North American plums are monophyletic. (3) Most North American plum taxa are para- and polyphyletic with respect to their chloroplasts---more than one of the three primary chloro-haplotypes was observed in 12 of 17 of the North American plum taxa. (4) Most North American plum taxa are not monophyletic with respect to their nuclear encoded s6pdh genes---three primary haplotypes are shared among most taxa. Total evidence provided by this investigation strongly supports the hypothesis of the North American plums are a syngameon, or hybridizing species group.