I tend to go with natural grasses on my floating Island. I take what is in the yard and what is around the area and use them as a starting point. To me if you add non native plants on the island it just looks kinda strange. Thats why I went with natural plants.
--------------------------------- 1/10 - 1/4 acre pond plus 16 ft deep/ Plus 40 ft by 20 ft by 6 ft deep koi and fathead minnow pond next to it. Upstate NY