This name is a synonym of Rhododendron mekongense var. melinanthum (Balf. f. & Kingdon-Ward) Cullen.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 12304887) with original publication details: Notes Roy. Bot. Gard. Edinburgh 9(57–58): 98–100 1920.
This name was in version 1 of The Plant List, record tro-12304887, and has not been changed.