TheArnica angustifoliaaggregate is a circumpolar taxon previously consisting of a number of geographically distinct infra-specific taxa. Cluster and principal component analyses of 99 populations revealed the aggregate to be best represented by two subspecies:A.angustifoliasubsp.angustifolia(a combination of the previously recognized subspeciesangustifolia,attenuata,sornborgeri,intermedia,iljinii, andalpinaandA.plantaginea) andA.angustifoliasubsp.tomentosa.Arnica angustifoliasubsp.angustifoliais polymorphic and varied in ploidy level and foliar flavonoid chemistry. No significant differences were found among the means of 14 characters in plants collected from six broadly delimited geographic areas. Four cytotypes (2n = 38, 57, 76, and 95) and seven flavonoid glycosides (five flavonols and two flavones) were discerned. The aggregate is predominantly agamospermous with amphimictic phases in unglaciated Alaska and west central Yukon. Disjunct distributions are probably the result of survival in refugia during the late Wisconsinan.