If the actual stem is red or reddish which it appears to be then it's Red Nesaea. When it has a red stem it's in it's emersed growth form. As it changes to it's immersed form the stem will lose the red color but if there is enough light the leaves will remain red. This is a high light plant that does best with CO2 and a dry fert dosing regime like PPS-Pro or EI.