A crossing program was carried out between the Kauai endemicB. forbesii and six other Polynesian species, five of which are Hawaiian and one Marquesan. All crosses produced vigorous F₁ hybrids, portraying a strong genetic relationship betweenB. forbesii and the other species. The results indicate a close systematic relationship among the Polynesian species ofBidens placed by Sherff in sect.Campylotheca and strengthen the argument that this group dispersed from North America to the Hawaiian Islands, then from Hawaii to the Marquesas Islands.