The other day, a friend and I went for a road trip to the southern Louisiana coast, in St. Mary parish, just north of Marsh Island, at a state park on Vermilion Bay. I found Sweet Acacia growing right next to salt water. I also found bundleflowers growing on the back side of the beach in the longish grass. So apparently, both bundleflowers and sweet acacia can grow in coastal regions that, recently, from time to time, have been inundated with storm surges from tropical storms and/or hurricanes, as some of the bundleflower plants appeared to be at least a few years old, and the same with the sweet acacias.
I collected many bundleflower seeds, and many sweet acacia seed pods laying on the ground under three or so trees who grow together.