This name is a synonym of Rhododendron cinnabarinum var. roylei (Hook. f.) Hutch..
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 50156513) with original publication details: Rhododendron Sikkim Himalaya 1: , pl. 7 1849.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:333254-1.
This name was in version 1 of The Plant List, record tro-50156513, and has not been changed.