Hello Aaron, Here in my pond I grow Polygonatum amphibium. It is not tuberous, but it is an interesting aquatic plant that can grow in various conditions, hence its name. In deep water it will root in the mud and send up wiry shoots to the surface where the leaves will float, it can flower this way, the flowers are held upright or at an angle above the water surface. In low water or moist soil it will look like a herbaceous perennial which it is. It can also flower this way. Mine is grown the floating way, in a pot as it tends to spread more than I like. It is native to Germany but not common. You are welcome to a piece. Greetings from Germany, cold, windy and rainy just above freeezing here, very comfortable outside...... Uli