I have seen these and photographed them before. I am assuming they are both L. palustris
, but I don't know for sure. The more common one tends to produce narrow leaves when submersed and when it is cool. It also tends to be redder. The less common one does not change leaf shape much when submersed and it tends to stay green. Some pictures:
The plant in the upper right corner has got to be genetically different from the others.
The difference between the red ones with smaller leaves and the green ones with larger leaves is especially apparent in the shaded portion of the picture.
Today I collected both of them, gave them the bleach treatment (2 min.) and they are now planted. We will see if they continue to look different under aquarium conditions.