This name is a synonym of Sparganium erectum subsp. neglectum (Beeby) K.Richt..
The record derives from WCSP
(data supplied on 2012-03-26)
which reports it as a synonym (record 351118) with original publication details: Fl. Galicia 3: 412 1909.
This name was in version 1 of The Plant List, record kew-351118, and has not been changed.