This name is a synonym of Begonia polygonata Liebm..
The record derives from WCSP
(data supplied on 2012-03-23)
which reports it as a synonym (record 460332) with original publication details: Prodr. 15(1): 312 1864.
This name record (from WCSP) was not included in version 1 of The Plant List. It is possible the same name was included from a different data source, to check this you can search for Begonia polygonata in version 1 of The Plant List.