Morphological and Molecular Approaches to Disentangling the Taxonomy of Plumeria Species (Apocynaceae)

This dissertation investigated the taxonomy of Plumeria, a popular ornamental plant in the Apocynaceae. A brief introduction to the plant and its current taxonomy is provided in Chapter 1 along with a proposal for research to identify Plumeria spp. by morphological and molecular approaches. The overall goal of this research was to evaluate morphological and molecular characters that are useful for identifying Plumeria spp. so that we can delineate species boundaries, verify our taxonomic understanding of Plumeria, and begin to understand their evolutionary history. The use of qualitative and quantitative morphology to diagnose Plumeria spp. from the literature is difficult because of the multitude of descriptions given by various authors, even for the same species. Furthermore, the criteria for delineating currently recognized Plumeria spp. is unclear. Hence, in Chapter 2 the use of descriptive morphology is evaluated to determine its effectiveness at identifying Plumeria spp. Using iterative principal component analyses, it was found that a combination of descriptive vegetative characters was useful for identifying most Plumeria spp. However, other species could not be identified based solely on descriptive morphology, due to morphological variation of descriptors used. Instead, it would require the use of quantitative measurements and the use of other morphological characters, such as fruits and flowers, to properly diagnose these species. Chapter 3 explores molecular approach to delineating species and investigates the phylogenetic utility of five candidate loci. Some regions were able to identify operational taxonomic units as true species, but no single region could be used to identify all the putative species in our sampling. In fact, not all species could be recovered as distinct clusters even with a data set that combined four molecular regions. On the other hand, it did result in a well resolved phylogeny that agrees with prior findings, notably that most Plumeria are distinguishable by molecular means and that some Plumeria form a species complex comprised of morphologically variable members that share very similar molecular characters. Chapter 4 concludes with a synthesis of morphological and molecular findings and future directions in the realm of disentangling the taxonomy of Plumeria spp