This name is a synonym of Nuphar polysepala Engelm..
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 22600225) with original publication details: J. Elisha Mitchell Sci. Soc. 72(2): 339 1956.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:171079-2.
This name was in version 1 of The Plant List, record tro-22600225.