Using molecular phylogenetics to unravel morphological shifts, niche transitions, and geographic expansion at two different scales in the plant genus Oxalis (Oxalidaceae)

The plant genus Oxalis (Oxalidaceae) is rich in species and vegetative morphological diversity, and its species occupy diverse biomes and geographic zones. This dissertation employs molecular phylogenetics to infer some of the historical processes that led to extant Oxalis diversity.;In chapter one, I infer the first representative molecular phylogeny of the entire genus using plastid trnL-trnL-trnF, trnS-trnG, trnT-trnL, psbJ-petA, and nrITS sequence data. To explore the evolutionary histories of succulence, biome preference, and geographic distribution within the genus, I reconstruct their ancestral states and transition rates. I infer that early Oxalis lineages were non-succulent occupiers of mesic forests in southern or eastern South America, and find higher transition rates among succulent morphology and biomes than geographic zones. This suggests that adaptive radiation may be a useful model for many Oxalis lineages, and that phylogenetic biome conservatism may play a limited role in Oxalis.;In chapter two, I focus on a clade of the genus that I call the American bulb-bearing Oxalis. Using similar sequence data, I constructed phylogenies for the group, finding that it contains members of sections Ion Oxalis and Pseudobulbosae. It includes one clade that occupies southeastern South America and another in the Andes, with at least two dispersals to North America. Additionally, I found that transitions away from tristyly have occurred on several occasions, but that the majority of distylous North American species belong to one clade.;In chapter three, I explore the morphological correlates of environmental preference of the American bulb-bearing Oxalis. I infer a new phylogeny for the clade to x sample additional species and structure a comparison of quantitative and semi-quantitative environmental and morphological data from georeferenced herbarium specimens. Evolutionary models for most of the environmental and morphological traits reveal very little phylogenetic signal, and some aspects of storage morphology are correlated with precipitation and seasonality factors, suggesting an adaptive role for morphology in this clade.