This name is a synonym of Zannichellia palustris subsp. pedicellata (Wahlenb. & Rosén) Hook.f..
The record derives from WCSP
(data supplied on 2012-03-23)
which reports it as a synonym (record 460673) with original publication details: Quatre Fl. France 134 1935.
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 Zannichellia palustris in version 1 of The Plant List.