A threatened wetland plant that lives only in the floodplains of the Ilinois River has only 12 populations scattered over a distance of 250 miles. The plant has seeds highly adapted to floating long distances on floodwater. The Illinois River is also known for reversing flow during extreme flood events, providing multiple ways for seeds to land in different areas.

A recent study examined the genetic diversity within and among this plant's populations. Astonishingly, the scientists discovered there was still a high degree of diversity with substantial genetic similarity between the populations even though they were widely separated. What could explain this result?

A. Unique mutations had occurred in each of the 12 populations.
B. Overall gene flow maintained the genetic diversity of the populations by actively transferring aleles among the remaining groups
C. The similarity was a result of gene flow that had occurred via seed dispersal on the river.
D. Dispersed seeds germinated and then pollinated plants in other populations, resulting in gene flow.
E. Genetic bottlenecks had occurred in all of the populations.