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 12304765) with original publication details: Notes Roy. Bot. Gard. Edinburgh 13(65): 292–293 1922.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:333326-1.
This name was in version 1 of The Plant List, record tro-12304765, and has not been changed.