I've spent some time trying to find this plant, closest I can find as far as leaf shape would be some of the vals but they don't seem to grow a "stem," they are all leaf if that makes sense. Some of the giant hygro looks close but this plant is rounded at the top tip, where as most of the hygros are pointed. Along with the "veins" of the hygro come of the center vein at angles and this plant seems to have veins that come of the center fairly close to perpendicular.
A lot of folks have checked out the pictures, no ideas? I hope my description helps!
Here we go, I moved my light around a bit to get a better shot!
Back in March the best guess was an aponogeton of some sort. I used to have several A. longiplumulosus though they slowly dwindled down to one bulb that puts out a few leaves from time to time. That is in a totally different area of the tank. I believe this came in as an extra with the very first batch of plants I purchased here on TPT!
I didn't realize there were hybrids like AirstoND said. No wonder there isn't too much info on them. This lfs usually just takes the word of their supplier on what they are selling. They also sell some non aquatic plants as aquatic. But they have the friendliest workers.