Very cool - I got some frogbit a few weeks ago and it has done great. Are these a type of frogbit? The roots seem to be much fuller than the frogbit - I'll bet they are great filters for your tanks.
Red root floater is May's plant of the month on AC, and BK718 wrote up a great article. Lots of pics, including a side-by-side comparison of RRF and frogbit.