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 26002587) with original publication details: Kongl. Svenska Vetensk. Acad. Handl., n.s. 13(1): 132 1971.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:888619-1.
This name was in version 1 of The Plant List, record tro-26002587.