The Ceratopteris, I used to grow (long ago) was called cornuta. The one I grow now is called thalitrichoides.
They may well be variations of the same species.......but in that case, there is quite big differences to be aware of.
C. cornuta grew quite well submersed with no added CO2 and had very broad leaf-plates.
C. thalitrichoides does - for me - not really grow well submersed without some added CO2 and has rather slim leaf-plates.
Colour of the cornuta was more "yellow-transparent-ish-green" whereas thalitrichoides is more "grey-ish green". This is very small nuances, ofcourse, both being bright, light green.
Both actually prefere a life as a floating plant, but I have never seen cornuta produce emerse leaves as "skinny" as thalitrichoides does.
- none the wiser, I know.......but those are my observations of differences in the two.