This name is a synonym of Rhododendron sanguineum var. didymoides Tagg & Forrest.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 12304711) with original publication details: Notes Roy. Bot. Gard. Edinburgh 13(61): 51 1920.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:332852-1.
This name was in version 1 of The Plant List, record tro-12304711, and has not been changed.