Floristic Elements and Floristic Areas of North America defines floristic elements and biogeographic areas across the continent using principal components analysis (PCA) of 245 local floras from Canada, the United States, and Mexico. Three complementary analyses were conducted: (1) PCA of Otsuka similarity indices based on shared species, identifying 27 floristic subprovinces; (2) PCA of Pearson correlations on the logarithm of species per genus, identifying 12 floristic provinces; and (3) PCA of Pearson correlations on the logarithm of species per family, identifying 4 major floristic regions.

The results demonstrate that 78% of the 245 floras form nested hierarchical groups across all three analyses, and 98% form nested groups at two hierarchical levels. When compared with earlier biogeographic systems by Dice, Udvardy, and Cronquist, McLaughlin’s findings support elements of each but show that none fully capture the major floristic patterns of the North American continent. This study provides a quantitative framework for understanding large-scale floristic relationships and regionalization.