This name is a synonym of Rumex japonicus Houtt..
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 50136101) with original publication details: Bot. Mag. (Tokyo) 8: 174 1894.
This name was in version 1 of The Plant List, record tro-50136101, and has not been changed.