This name is a synonym of Crataegus marshallii Eggl..
The record derives from RJP
(data supplied on 2011-10-18)
which reports it as a synonym (record 18639) with original publication details: Viaggio negli Stati Uniti Viaggio negli Stati Uniti; 1790 292 1790.
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 Mespilus oxyacantha in version 1 of The Plant List.