DETLING, LEROY E.2016-08-022016-08-021968-0700786047https://hdl.handle.net/1794/2000666 pagesThe modern flora of the Pacific Northwest is characterized by associations which show affinities to floras now occupying widely separated areas (Eurasia, South and Central America) and to floras shown by paleobotanical evidence to have occupied all these areas, but particularly the American West. Distinct distribution patterns, both in time and space, manifest themselves. These patterns are and have been influenced by topographic and climatic changes from the Cretaceous to the present. Three principal sources of associations are evident: evolution in situ; northern regions as shown in the Arcto-Tertiary Geoflora; western Mexico and the southwestern United States as shown in the Madro-Tertiary Geoflora.en-USCreative Commons BY-NC-ND 4.0-USFloraPaleobotanicalArcto-Tertiary GeofloraGeofloraCretaceousMadro-Tertiary GeofloraMadro-TertiaryArcto-TertiaryArticle