Systematics, Inflorescence Evolution, and Leaf Anatomy in the Neotropical genus Varronia (Boraginaceae)

Boraginaceae Juss., with ca. 2,500 species are distributed worldwide. Many occupy xeric or seasonally dry habitats in tropical and temperate biomes. This dissertation focuses on the genus Varronia to understand patterns and processes of evolution in neotropical habitats.;Chapter one addresses aspects of phylogenetic relationships that remain elusive: among Boraginaceae and between Boraginaceae and other asterids. A matrix of chloroplast markers was assembled. Phylogenetic inference and hypothesis testing eliminated Gentianales as the closest relative to Boraginaceae but could not eliminate Solanales, Lamiales, or Vahlia. Among lineages of Boraginaceae, monophyly of Hydrophylloideae cannot be rejected and paraphyly of Ehretioideae with respect to the parasitic Lennoiodeae is supported. Taxonomic implications for Boraginaceae are discussed in the context of these results.;The second and third chapters focus on Varronia (Boraginaceae), a genus of ca. 125 species distributed from Arizona to Argentina, occurring in a variety of biomes. Species richness is especially high in biodiversity hotspots in Mexico, Brazil, and the tropical Andes. Most species of Varronia exhibit heteromorphic self-incompatibility, requiring pollinators to move pollen between flowers. Inflorescence architecture is a key factor in floral display and attraction of pollinators that are essential for reproduction. In the typical cymose inflorescence, the apical meristem becomes a single, terminal flower, and branching occurs via lateral meristems. In Varronia, morphological evolution modifies a cyme into spikes, and clavate or globose capitula. Taxonomy within the genus has relied on inflorescence morphology to delimit sections within the genus.;Chapter two presents the first densely sampled molecular phylogeny for Varronia. A matrix of inflorescence types is used to address hypotheses regarding inflorescence evolution and to evaluate the taxonomic utility of inflorescence traits. Results show remarkable evolutionary vagility in inflorescence type.;In chapter three, most species of Varronia are examined for leaf structure and micromorphology. Ancestral states of these characters along with habitat types are reconstructed to evaluate the relative importance of evolutionary and ecological forces in shaping diversity among species. Results demonstrate that much of the foliar variation documented corresponds to changes in habitat type, and not with phylogenetic relationships.