This is a Fragrant Water Lily, Nymphaea odorata. It's one of approximately 36 species in the genus, itself one of 7 or 8 genera in the family Nymphaeaceae. According to the Flora of North America website, this is one of 9 species of Nymphaea that occur in North America.
The entire family is often referred to as water-lilies, of course, since they are entirely aquatic. They grow rooted to the bottom of ponds and slow rivers, with leaves submerged, emergent, or floating on the surface. The flowers are raised above the surface to some degree, as seen here:
In addition to their beauty, and their ecological importance in warm wetland areas, water lilies are of interest to botanists because of their taxonomic position. They are generally thought of as the second most basal group of angiosperms, branching off from the other flowering plants just after Amborella did so. A recent paper, however, argues that Amborella is the sister group of a Nymphaeaceae - Hydatellaceae clade. (Hydatellaceae is a small family of minute aquatic plants.) This means that the water lilies are direct descendants of that first branch off the flowering plants, basal to all of the other angiosperms.
Water lilies and Hydatellaceae are aquatic plants, but Amborella is a land plant, as are most of the angiosperms. So: were the original angiosperms aquatic, with Amborella climbing onto land, or were they terrestrial, with the water lilies aquatic preference evolving after that next split?
In a similar vein, Amborella has vascular tissue that is missing certain elements normally found in angiosperms (one reason why they've been considered a basal group). But if they're in a clade with two or three other families that do have that tissue, did they somehow lose those elements? Or is this an interesting case of convergent evolution between the Nymphaeaceae and the rest of the angiosperms?
, , , , , , , , , and Syst Biol (2013) 62 (1): 50-61 first published online July 31, 2012 doi:10.1093/sysbio/sys070
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