This name is a synonym of Rhododendron maddenii subsp. crassum (Franch.) Cullen.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 12303779) with original publication details: Bull. Soc. Bot. France 34: 282 1887.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:332255-1.
This name was in version 1 of The Plant List, record tro-12303779, and has not been changed.