How does a wildflower native to Switzerland get to Montana

Water dispersed seeds of the wildflower.

There are many possible ways.

As the other user said before, transportation by water is a feasible method.

Modern technology has also increased chances of seeds being spread. Seeds could easily be stowed on people's clothes, on ships, airplanes, etc.

Also, many places may cultivate this wildflower in Montana, possibly exposing the land to its seeds.