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 460671) with original publication details: Comp. Fl. Ital. 643 1882.
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 dentata in version 1 of The Plant List.