I got some fossil specimen resembling the genus Vallisneria from early Cretaceous sequence of India. However, now the problem is, molecular age estimates shown that the family (Hydrocharitaceae) itself originated around 75 Mya (Crown node) to 88 Mya (Stem node) (Janssen and Bremmer 2004). The specimen which we recovered is going back to 125-135 Mya.
Dear Chinnappa, I would advice you to contact directly with some of the following Cretaceous researchers, working with Early Cretaceous aquatic plants: e.g. - Bernard Gomez,Véronique Daviero-Gomez,Clément Coiffard, Carles Martín-Closas,and David L. Dilcher, recently they described Montsechia, an ancient aquatic angiosperm. Sincerely, S. Vikulin
e.g. http://www.researchgate.net/profile/Veronique_Daviero-Gomez
etc.