Umm, I'm pretty sure it is Alternanthera Reineckii. I'm not good with scientific names at all. I only remember what the labels said the more common names are. Although when I search 'Alternanthera Reineckii' it pulls up variations of this plant, but its the scientific name that fits it closest.
Wow I just bought some of these from petsmart. LOL! they sell it in an airtight package with agar gel to keep the plants from dehydrating + nutrition. o_O I planted them outside in my outside tank... I hope they'll do fine o_O