This name is a synonym of Crataegus ambigua C.A.Mey. ex A.K.Becker.
The record derives from RJP
(data supplied on 2011-10-18)
which reports it as a synonym (record 18762) with original publication details: Flora USSR Flora USSR; 1934 443 1939.
This name record (from RJP) 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 Crataegus sororia in version 1 of The Plant List.