@ Nevin, so far I know it brought to North America from Europe in 17th Century.

Looking to the introduction of white clover from Europe to the New World I think we need to consider that white clover might be most likely introduced in the manure of imported cattle. White clover has hard seed which likely survives the bovine digestive track. Man cattle and clover could be seen as co evolvers in some sense. Each colony power imported different cattle into the New World. Columbus and Ponce de Leon are considered to have transported cattle to Dominican Republic Mexico and Florida. The English introduced cattle in Massachuets French, Dutch, Portuguese and Danish also introduced cattle. In North America in English white clover is known as Dutch White Clover the white clover is Eurasian origin and not native to New World. I suggest its introduction may not have intentional but related to the cattle importation and the white clover may well have been a hitch hiker of sort. I imagine that conscious seed propagation of forages followed the importation of cattle and the cattle was prime consideration. While cattle were introduced starting in 1500's for Spanish and 1600's for English it was probably not until 1700's or later that organized seed productions were considered and imported. Some thoughts.