Aperture evolution in Nymphaeaceae: insights from a micromorphological and ultrastructural investigation

The evolution of the apertural type in the ANITA-grade family Nymphaeaceae, despite the importance of pollen characters for both palaeobotanical and neobotanical investigations, has not been yet totally understood. To elucidate some unclear aspects regarding the homologies of the apertural condition in basal and core Nymphaeaceae, we examined the pollen grains from five species of this family. We offer for the first time some evidence about the presence of a proper operculum in the pollen grain of Nuphar and for the ring-like status of the aperture of Nymphaea caerulea and Victoria cruziana. Our findings clarify and reinforce the hypothesis of an opercular origin of the distal part of the pollen grain in the core Nymphaeaceae and support the paraphyly of the genus Nymphaea as emerged from recent molecular studies. The diversity and specialisation of this 'basal' family is underlined even by its pollen characters. © 2013 Copyright Collegium Palynologicum Scandinavicum.