They're two different forms of water sprite (thalictroides) and ( cornuta). You have the former which prefers to planted in the substrate but can be floated but I had absolutely no luck with it. It works for some and not for others. As for cornuta it is the floating form which is pretty hard to find unless you purchase from maybe aquabid. Byron said this is one of the easiest plants to grow once established as it grows fast and sucks up ammonia.
I have some planted and floating Ceratopteris thalictroides. Although the planted ones aren't doing so well right now, the floater is doing fine up at the surface. At the height of my tank's health, the planted plants showed a phenomenal growth, growing up through the canopy near the cutout for the filter.
I bought them as a bunch 10 inches long and I noticed their claw-like roots - very thick and sturdy. I put them in the substrate.
The one that is floating is showing itself to be very hardy because the subfronds look like they're glued onto the bottom of the water surface. Although being attacked by cyanobacteria (BGA), the healthy fronds are able to keep from being totally engulfed.
The thing that I like the least about this plant (a true fern) is that you can't just trim it, an entire frond must be cut off if one is to avoid a lot of brown ends.
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