This name is a synonym of Vallisneria natans (Lour.) H.Hara.
The record derives from WCSP
(data supplied on 2012-03-23)
which reports it as a synonym (record 453841) with original publication details: Acta Phytotax. Geobot. 22: 74 1966.
This name record (from WCSP) was not included in version 1 of The Plant List. It is possible the same name was included from a different data source, to check this you can search for Vallisneria gigantea in version 1 of The Plant List.