"Radicans" is an old name that used to be associated with Echinodorus macrophyllus, a very robust and large sword plant. It will grow under medium light such as you have, but will do so faster under brighter light - of course, you may not want that, it can be a very domineering plant. Echinodorus cordifolius is also sometimes called "radicans" as well, a similar but slightly smaller plant.
As for the plec, don't know, most plecs I have kept don't eat healthy plants. They may take algae off the leaves, or eat a rotting leaf though. If you know what type of plec it is, I'd ask the folk on the catfish board if that is typical behaviour.