I wish I knew. I'm horrible at remembering names of plants.
My 20 gallon high came with some Elodia (the woman who sold me the tank gave me some clippings for free) - although, the elodia is not in the 2.5 g tank... I'm using it as a floater in the 15g and 20g long. ...
The plant that is doing so well in that small tank though came from somebody selling clipping on the aquatic plant website. I don't know what the plant is, but it's really hard to plant it - the stems are extremely delicate and the simple act of pinching the lower leaves off will sometimes take the stem with it - very pain in the butt plant - but, for whatever reason it really thrives in that tiny tank.
The floater that I used in the small tank is called 'watersprite' and it grows really well, but in every big tank that I've put it in - it's prone to growing masses of algae in it - algae that is so thick and sludgelike that I more often than not, end up tossing it ... I'm new to planted tanks and two of my large tanks have lights that are too strong for the low-tech method. I'm cringing to add CO2 to my tanks though... I don't feel like I'm quite there yet, research wise.
Live plants are really a difficult beast to master, although the fish love them. Each of those tanks are far from being 'landscaped' masterpeices. But, the fish don't seem to care...