Need another ID

Here's another plant I collected and was curious if anyone might have an idea as to what it is. It was in a shaded and stagnant ditch, both above and below the waterline (no more than 10" or so either above or below it).



From above:



Here's the tank it's in (along with some H. zosterfolia) and it seems to be doing pretty well--putting out quite a bit of growth:



Any ideas?