This name is a synonym of Linaria oblongifolia subsp. aragonensis (Lange) D.A.Sutton.
The record derives from WCSP (in review)
(data supplied on 2012-03-23)
which reports it as a synonym with original publication details: Prodr. Fl. Hispan. 2: 569 1870.
This name record (from WCSP (in review)) 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 Linaria diffusa in version 1 of The Plant List.