This name is a synonym of Achillea ageratifolia subsp. serbica (Nyman) Heimerl.
The record derives from TICA
(data supplied on 2012-02-11)
which reports it as a synonym (record D39A746F-7C2B-4B6F-BFD1-1AE2B02B80C1) with original publication details: Consp. Fl. Eur.: 364 (1879) 364 1879.
This name was in version 1 of The Plant List, record gcc-14488, and has not been changed.