This name is a synonym of Rhododendron stewartianum Diels.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 50060640) with original publication details: Rhododendron Year Book 6: 177 1951.
This name was in version 1 of The Plant List, record tro-50060640, and has not been changed.