This name is a synonym of Cephalanthera longifolia (L.) Fritsch.
The record derives from WCSP
(data supplied on 2012-03-23)
which reports it as a synonym (record 454865) with original publication details: Suppl. Pl. 404 1782.
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 Serapias grandiflora in version 1 of The Plant List.