This name is a synonym of Rhododendron thomsonii subsp. lopsangianum (Cowan) D.F. Chamb..
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 12304850) with original publication details: Notes Roy. Bot. Gard. Edinburgh 19(94): 250–251 1937.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:332797-1.
This name was in version 1 of The Plant List, record tro-12304850, and has not been changed.