This name is a synonym of Rhododendron arboreum var. cinnamomeum (Wall. ex G. Don) Lindl..
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 50060262) with original publication details: Sp. Rhodod. 15 1930.
This name was in version 1 of The Plant List, record tro-50060262, and has not been changed.