Systematics and evolution of Nymphoides, the "other" water lily (Menyanthaceae)

Flowering plants have evolved to occupy aquatic habitats repeatedly, taking advantage of reduced competition due to the difficulty of adapting to such environments. Although water is abundantly available, aquatic plants must deal with the challenges of transporting gases and in many cases obtaining light or nutrients where they are in short supply. Many types of growth habit exist, including plants that grow in inundated wetlands, some that are entirely submersed, and some that float on the water surface. One growth form in particular, that of the rooted, floating-leaved habit, allows plants to take advantage of soil nutrients while obtaining sunlight and gases directly from the atmosphere. One of the more recognizable plants employing this growth habit is Nymphaea, the water lily, in the family Nymphaeaceae. Another, lesser-known but truly fascinating group of floating-leaved plants comprises species in the genus Nymphoides. These plants likely first evolved in Australia, from a small group of wetland-dwelling ancestors, and from there they have diversified and spread throughout the world. The study of Nymphoides offers insights into many significant evolutionary questions, such as how plants evolve the floating-leaved vegetative habit and how they overcome challenges associated with growing in water. Using a phylogenetic tree of relationships within Menyanthaceae, I have been able to reconstruct the biogeographical history of the family and the probable course of morphological evolution, including the general vegetative habit and the architecture of inflorescences, which are highly modified in some Nymphoides species.