Taxonomy and distribution of Clematis, sect. Atragene (Ranunculaceae), in North America

Two North American species ofClematis, sect.Atragene (L.) DC, are recognized.C. occidentalis (Hörnern.) DC. is divided into three varieties, native respectively to eastern North America, the Rocky Mountains, and the Cascade Mountains of Washington.C. columbiana (Nutt.) Torr. & Gray is divided into two extensively intergrading varieties, one prevailing in the southern Rocky Mountains, the other in the northern foothills and in outlying mountain …