This name is a synonym of Rhaponticum longifolium (Hoffmanns. & Link) Dittrich.
The record derives from TICA
(data supplied on 2012-02-11)
which reports it as a synonym (record 75DC7DED-ABA3-467B-9DF1-3FB3CB9FF1DC).
This name record (from TICA) 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 Centaurea longifolia in version 1 of The Plant List.