It took me nearly ten years to collect these species, which can be identified as three species, including one of them containing four different types.
Here is the popular one, C.thalictroides, a submerged type.
This one has been recently identified as a varieties of C.thalictroides from Vietnam, which can grow very large leaves and keep submerged much longer than the former. I will say that this plant is the most delicate one of the genus.
The third one is also found in northern Taiwan. There are lots of rumors that C.cornuta can be found in Taiwan, while I don't think so, this rumored local species tends not to grow submergedly, and we can find many differences on its leaves (especially the growing point) from those of C.cornuta.
Although the aforesaid ones are all identified by our botanists as C.thalictroides I still doubt that the second type might be C.richardii because the feathery leaves growing just like those of C.richardii. Unfortunately I cannot prove it because I don't have a microscope to observe its spores.
Possibly the only floating species of the genus, C.pteridoides.
There are 4 to 6 species of the genus according to old literatures, so I think C.richardii and C.froesii could be the ones I have to search for.
This is an old picture, taken in 1969 and digitized by taking a picture of the original slide with my digital camera. This is only part of the slide image.
Enough apologizing for the quality of the picture. This is a Ceratopteris variety I had at the time with large leaves that had only a few incisions. Unlike Biker's picture of C. pteridoides, this plant did not develop swollen petioles. It is similar to Biker's plant in that it has large leaves that are not deeply divided and that it prefers to grow floating. My plant was different in that the leaf edges were rounded and the petioles were not swollen.