Acknowledgements

We are very grateful for additional data and literature references sent by Dr. J.F. Veldkamp (L), Dr. R. Clarysse (BR), the Center for Aquatic Plants, Gainesville, Florida, USA, T. Beeckman (GENT) and Konraed Camelbeke (GENT).

Thanks are also due to Adelin Van Heuverswijn (GENT) and Dirk Rosseel (GENT) for their valuable technical assistance.

Finally we thank Prof. G. Ll. Lucas, Keeper of the Herbarium, Royal Botanic Gardens, Kew and Prof. P. Van der Veken, Director of the Laboratory of Plant Morphology, Systematics and Ecology, University of Gent, for their generous support of this journal.