This name is a synonym of Brachythecium plumosum var. perrobustum Sakurai.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 35114821) with original publication details: Trans. Sapporo Nat. Hist. Soc. 13(4): 394 1934.
This name was in version 1 of The Plant List, record tro-35114821, and has not been changed.