Systematics and Evolution of Menyanthaceae and the Floating-Leaved Genus Nymphoides

Menyanthaceae (70 species) are a family of aquatic and wetland plants that occur worldwide. This diverse group contains different growth habits (emergent and floating-leaved), reproductive systems (heterostyly, homostyly, gynodioecy and dioecy), floral and seed morphologies, and inflorescence architectures. In this study, I have evaluated the phylogenetic relationships, taxonomy, biogeography, and morphological character evolution for over half of the approximately 50 Nymphoides species, plus all species in related genera within the family. ^ In Chapter 1 I investigated generic relationships across Menyanthaceae and found that the contemporary circumscription of Villarsia included three paraphyletic lineages that graded toward a monophyletic Nymphoides. Biogeographical reconstruction supported an Australian origin for the family and also for all of the major clades, with dispersal events corresponding to the boreal sister taxa Menyanthes and Nephrophyllidium, and the South African Villarsia clade. ^ Chapter 2 is a study of the genus Nymphoides that examined all Australian species of the genus and synthesized for the first time the morphological data for all the species worldwide. Morphological data analysis indicated several relationships, including the grouping of species with similar inflorescence habits. Molecular phylogenetic analyses supported a similar division, but species resolution was thoroughly incongruent on trees derived from nuclear (nrITS) or chloroplast (matK/trnK) data, suggesting widespread hybridization during the diversification of the genus. ^ In Chapter 3 I studied the Nymphoides inflorescence architecture, which comprises three types: expanded (pairs of flowers separated by internodes), condensed (single floating leaves each supporting a cluster of flowers), and a morphology unique to N. peltata (pairs of leaves supporting clusters of flowers). I determined that these quite different inflorescence types likely were derived from a common blueprint, from which they deviate only by their relative elongation of internodes or expansion of bracts into foliage leaves. ^ In Chapter 4 I examined the life history and reproductive potential of N. peltata, a Eurasian native that is naturalized in North America. Populations of N. peltata are able to produce abundant fruits with highly germinable seeds, but the plants are genetically identical throughout their naturalized range, possibly the result of inbreeding while in cultivation.