[Solid]

I collected this plant from a canal behind my parents house, here in Miami, FL. When i collected it, I only took some emergent stems because I didn't want any of the algae and stuff growing on the lower portions. The emergent leaves were round and it had a bright red stem (unfortunatly i don't have a picture). Since growing submerged it had grown light green and longer thinner leaves.

 

[sewingalot]

Based on its looks and your description of the emersed plant, it looks like a rotala roundfolia sp. to me.

 

[Tinanti]

Cold be R. rotundifolia (introduced, as is R. indica). Photos of emersed stuff would help.