Macroevolutionary patterns and processes of diversification in sedges (Cyperaceae), with emphasis on Eleocharis
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This dissertation includes three chapters, the first two of which focus on the genus Eleocharis--an ecologically and economically important group of sedges containing over 250 species, with centers of diversity in seasonally wet tropical to subtropical regions. In Chapter 1, we examine morphological evolution of stems in Eleocharis subgenus Limnochloa. In Eleocharis, the stems serve as the primary photosynthetic organs and as such their structure is presumed to affect photosynthetic efficacy. We identify a complex history of stem shape evolution characterized by a high degree of homoplasy and rapid rates of change, using stochastic mapping and Markov 1-rate models to infer evolutionary changes. Our data also suggest that changes in stem shape and anatomy may be associated with speciation (Pagel's κ = 0.3503, p = 0.04579). The second chapter focuses on intrageneric relationships in Cyperaceae, with emphasis on Eleocharis. We elucidate the relationships between Eleocharis and two monotypic genera--Egleria and Websteria--which we show to be included within Eleocharis. In addition, we clearly document a sister relationship between Eleocharis and the Abildgaardieae. A third questionably segregate genus, Chillania, could not be included in the molecular dataset, but its morphology suggests it should be included in Eleocharis. Supporting nomenclature is provided to place Chillania, Egleria, and Websteria in Eleocharis. The final chapter focuses on infrafamilial relationships within Cyperaceae, as well as the exploration of novel phylogenetic methods to reconstruct histories using sparse supermatrices mined from public nucleotide sequence repositories (in this case GenBank). We show that highly incomplete datasets can yield very good estimates of phylogeny, and we offer suggestions for ways to improve data decisiveness and phylogenetic utility of datasets by filtering taxa and genes. We present the best-resolved phylogenetic trees of the Cyperaceae that have been published to date, and we discuss their significance for sedge classification.