This name is a synonym of Rumex occidentalis S. Watson.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 50079663) with original publication details: Pittonia 4(25A): 304 1901.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:224439-2.
This name was in version 1 of The Plant List, record tro-50079663.