Arnica parryi in Flora of North America

Nature Talk
2

Looks like they just treat it as a synonym / don’t recognize it as a separate taxon:
http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=250066125

image

(as does POWO http://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:303234-2#synonyms)