Phylogeny and biogeography of Neotropical flowering plant tribe Citharexyleae (Verbenaceae)

Abstract

The New World tropics, or Neotropics, located within tropical latitudes of North and South America, are one of the most diverse ecoregion in the world. However, this diversity is poorly understood in terms of described biodiversity—species numbers are uncertain and collection records are depauperate for many groups distributed in remote locations or dense forest—and patterns of evolution contributing to high diversity—factors underlying speciation in lineages are not well understood. A molecular phylogenetic and systematic study of the Neotropical flowering plant tribe Citharexyleae in the Verbena family (Verbenaceae), which also originated and diversified primarily in the Neotropics, was undertaken in order to describe diversity and understand patterns of evolution in an understudied Neotropical lineage. Chapter 1 comprises a systematic study of tribe Citharexyleae, which describes relationships between the three genera in the tribe (Baillonia (1 species), Citharexylum (ca. 70 species), and Rehdera (2 species)) as well as relationships within Citharexylum, the largest genus. Baillonia is included in Citharexylum and Rehdera is retained distinct. A subgeneric classification including six subgenera system is proposed for Citharexylum, and morphological characters associated with each major clade described. In Chapter 2, the biogeographical patterns underpinning diversification in Citharexylum are explored. Citharexylum comprises ca. 70 species distributed widely throughout the Neotropics, from northern Mexico to southern Brazil and Argentina. Species occupy multiple biomes including continuously moist broadleaf forest, seasonally dry tropical forest, tropical coniferous forest, high elevation shrublands, and arid shrublands. The contributions of radiation within a biome and adaptation to/colonization of new biomes are compared. Both patterns have played important roles in the diversification of Citharexylum, and major lineages within Citharexylum display different patterns. The Mesoamerican clade exhibits a pattern of radiation within the ancestral biome with more recent, independent colonization events, whereas the South American clade exhibits a pattern of early colonization and radiation within biomes. Though diversification rates are higher in the Mesoamerican clade, both clades have produced similar taxonomic diversity in the same amount of time. Both patterns contribute equally to overall diversity in the genus. Chapter 3 incorporates molecular sequence data generated by the previous chapters with data generated in previous studies other lineages of Verbenaceae and newly generated data to produce an updated phylogeny of the Verbena family. Verbenaceae comprises ca. 770 species in 28 genera. A previous family-wide study sampled 7 chloroplast regions for 121 species. The expanded dataset encompasses twelve chloroplast regions, two nuclear ribosomal spacers, and eight low-copy nuclear loci for 366 species. Two new clades in Verbenaceae are described, including resurrection of the genus Scleröon Benth in Lindl.