The record derives from RJP (data supplied on ) which reports it as a synonym (record 15130) with original publication details: Hortus regius botanicus hafniensis. Supplement Hortus regius botanicus hafniensis. Supplement; 1819 52 1819.
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 odoratissima in version 1 of The Plant List.