We only have two Echinodorus in Texas, the less common berteroi
and the very common cordifolius
. It could be a submerged growing seedling of either. I'm going to assume you collected it in Hill County. You normally have to travel down to Georgetown before you start running into them, cordifolius that is, you have to go more north and west for berteroi, think Palo Pinto and then west.
Have a look, E. berteroi
Maybe you have a stray?