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 12304933) with original publication details: Notes Roy. Bot. Gard. Edinburgh 20(97): 72 1940.
This name was in version 1 of The Plant List, record tro-12304933, and has not been changed.