Carlos is correct. They are the same plant. Nanjenshan is the place where the plant (that may be a natural rotundifolia/wallichii hybrid) is found. "nanjean" is a spelling mistake. I have no idea why that site has the same plant labled with the correct and incorrect spellings in its emersed and submersed forms.
The plant was initially identified as Mayaca sellowiana. The name in parenthesis is not a synonym or alternative name of some kind. If you look at the Tropica web site, they have "Pellia" in parenthesis under the newer and correct name Monosolenium tenerum. I guess that's to help people get up to speed, so to speak.
I believe that Mayaca sellowiana is a valid species, just not that one.
If you check out the Tropica site, here's what it says:
"There is some uncertainty about the correct name of this plant. For some time it has been sold as Mayaca sellowiana, but actually this is Rotala sp. ''Nanjenshan'' (species unknown)."
I got some of the Tropica ones like the picture (with the pot), and it grew out to be like the other pic. I believe Tropica sells many plants in the emersed form. Mayaca sellowiana is an entirely different plant that looks similar.