The United States is unique among countries in that its
terrestrial ecoregions span three
biogeographic realms: the
Nearctic,
Neotropical, and
Oceanian realms.
Fifty states Alaska is the most
biodiverse state with 15 ecoregions across three
biomes in the same
realm.
California comes in a close second with 13 ecoregions across four biomes in the same realm. By contrast,
Rhode Island is the least biodiverse with just one ecoregion—the
Northeastern coastal forests—encompassing the entire state. The terrestrial ecoregions of the
50 states of the United States are as follows:
Five inhabited territories The ecoregions of the
5 inhabited territories of the United States are as follows: ==Marine ecoregions==