The phytogeographical characteristics of North America north of Mexico (NANM) were examined based on an analysis of the 1904 indigenous genera of the vascular plants known to the area. According to the worldwide distribution patterns of the genera, the 1904 genera were grouped into ten phytogeographical elements (categories). About 67.3% of the genera found in the native flora of NANM also occur in other areas of the world; of these, 71.4% occur in the Old World. About 32.7% of the 1904 genera are endemic to North America. The origins of the floristic relationships between North America and the rest of the world and the origin of the present-day flora of North America are discussed. The current floristic patterns of the NANM vascular plant genera resulted in part from palaeogeological events such as the unification of tectonic plates into a single supercontinent, Pangaea, and then the breakup of the united supercontinent into Laurasia and Gondwana followed by the fragmentation of Laurasia and Gondwana into individual continents as they are today due to the movement of plate tectonics. Many of the endemic genera of North America likely originated in the North American continent during the Tertiary, particularly during the uplifting of Rocky Mountains.