Th. arvense is illegitimate, as it was described with Th. linophyllon and Th. alpinum cited in synonymy, see https://www.ipni.org/n/780709-1

the legitimate name for these plants is Th. ramosum, which is listed as accepted at POWO
http://plantsoftheworldonline.org/taxon/urn:lsid:ipni.org:names:781073-1