Plant ID?

[Flyby Stardancer]

So a friend and I are trying to ID this plant she has in her tanks. One picture (http://fav.me/d6a14bo), and another (http://fav.me/d6a1b9w). (Both are links.)

It's a stem, grows like a weed for her, can be either rooted in substrate or floating, just needs one leaf to grow a new plant... It's nothing that she can figure out. Leaf conformation can change based upon unknown conditions.

Any ideas?

ETA: And some more pictures. One (http://fav.me/d6a19y0), two (http://fav.me/d6a1amt), three (http://fav.me/d6a1aud), four (http://fav.me/d6a1b2t).

[madagascariensis]

I think it's a hygrophila. Could be wrong.

[genocidex]

horn wort will also grow like that, so wont water wisteria

[Flyby Stardancer]

Okay, I've had the mystery plant in my tank for a couple days. Haven't seen much change in it, or the N-levels (beyond the normal changes that come from cycling the tank). I don't know if that's because the plants are still adjusting, or what.

Here's a pic from my tank.

29053
(There are a couple crypt leaves that got caught in the picture too, in the bottom right. :))

[Greentoads41]

I think it's water wisteria. I have seen it growing in four tanks I have around the house, and in each one it's a little different. The wayy it grows and the leaf shape Depends, in my observations, on depth of tank, lighting, substrate, CO2, nitrate levels, stem length, and other factors. It really does grow like crazy, and I like it alot.

[Flyby Stardancer]

Hygrophila difformis? All the pictures I've seen of it show leaves that are a lot more lacey, especially underwater.