Gleditsia is found in East Asia, on the East Coast of the Americas, and in South America; small populations of certain species also exist around the Caspian Sea (G. caspica) and India (G. assamica). There are native species to all these regions. The theory is that Gleditsia originated in East Asia in the Eocene, crossed the land bridge across the North Pacific Ocean into North America, and then spread down to South America millions of years later.[4]Gymnocladus is a sister genus of Gleditsia, and it too mimicked this dispersion pattern, except it came to the Americas much earlier.[4] Though there are no extant European Gleditsia species, there are fossils found in Europe which could mean that the genus also crossed the North Atlantic land bridge.[5]
Certain Gleditsia species are in clades with species from other continents; an example is G. caspica (from the Caucusus), G. delavayi, and G. japonica (both from Asia), who are in a clade together.[4]Gleditsia amorphoides is the most basal of the genus, most closely related to G. sinensis but not the North American species (G. aquatica and G. triacanthos).[4]
