Water Lettuce, Pistia stratiotes. One fall I brought it in from the Koi pond and it has grown profusely as a tank top plant. It is staying small, around 2-3 inches across, sends out runners like made. Its root system is huge, lots of refuge for babies. In koi ponds we use it to clean the water. In the tank it seems to be doing even better at cleaning. It will even outgrow and choke out duckweed. Being larger, it is easy to control. Once back outside come spring, it goes huge again. I would trade some to you for whatever is interesting. Denver local only, I am not into shipping. If you want to grow it, it takes lots of light. I am running one 48" florescent tube on each tank for about 14 hours a day. It likes 76-82 degrees, and it likes being splashed by power heads. Photo below is some of the smaller plants, only 1-2" across. Plants get more grey as they get larger. It does limit light penetration if you don't control it.