We sold something that looks like that at the aquarium shop that I used to work at. It was called Purple Waffle. As far as I know it is not a true aquatic plant. Watch the plant and see if it stays ok and does not start to rot.
Thanks. it's lace rock. I actually had it before anything else lol. I had had smaller pieces but when I saw that one at the store I couldn't resist. its actually hollow underneath. I originally got it figuring it would make a great natural cave for the loaches (which ironically I ended up not even moving into the new tank) I think I have shot somewhere showing underneath it. IT started out much whiter, but I kinda like the tone it turned once the lights and all were up and running.