The origin, phylogenetics and natural history of darwiniothamnus (Asteraceae: Astereae), an endemic shrub of the Galapagos Islands

Darwiniothamnus (Asteraceae:Astereae), one of seven plant genera endemic to the Galipagos Islands, has until recently had an unknown origin, number of species, and conservation status. The purpose of this master's thesis was to determine the origin and phylogenetics of Darwiniothamnus and to outline the major ecological factors influencing the survival of this genus. Material for this thesis was sequenced from the ITS (Internal Transcribed Spacer) region of 18-26S nuclear ribosomal DNA of putative sister taxa from South, Central and North America, Mexico and the Caribbean. A molecular phylogeny was then constructed using fifty-four representatives from the tribe Astereae. Sequence data suggested that Darwiniothamnus is polyphyletic, nested within the paraphyletic Erigeron-Conyza complex, and stems from two separate introductions into the Galapagos. Additional information regarding the current biological threats on extant populations of Darwiniothamnus, nomenclatural suggestions for potential new taxa, and hypotheses on the disjunct distribution of Darwiniothamnus throughout the archipelago are also provided within the thesis.