This name is a synonym of Buxus microphylla var. riparia (Makino) Makino.
The record derives from WCSP (in review)
(data supplied on 2012-03-23)
which reports it as a synonym with original publication details: Bot. Mag. (Tokyo) 26: 293 1912.
This name was in version 1 of The Plant List, record kew-2688015, and has not been changed.