Please ID this plant

this looks more like the first sugestion to me! Ammania gracilis.

the Ludwigia repens has rounder leaves.
the ludwigia arcuata has much thinner leaves.

but i am no expert and maybe it could be because of the conditions the plant is grown in and if thats the case i would more lean to the repens.

nice plant though
 
I'm pretty sure it's L.repens. L.arcuata has more needle shaped leaves like in this pic of mine.Not that it matters as the care is pretty much the same.L.arcuata is a little more fussy but both are pretty easy.

lud.jpg
 
This is a close-up of Ammania in my tank.Im sticking with L.repens.There are many cultivars of L.repens.Some have round leaves while there are others with lance shaped and even needle like as in L.arctuata.But,I could be wrong as well.The fun is in the pursuit...Cheers...

amma.jpg
 
I have what I believe is Ludwigia repens, too, under moderate light conditions (28W/10,000K over 10G, in a coralife fixture). It's green on top of leaves, red on bottom of leaves. Sat around and just... "was" (in a Zen fashion) for months and months and months, then decided it liked its situation and has been growing well since Spring, putting out roots and not minding being trimmed and the trimmings being replanted. I like the plant a lot. Mine has a bit rounder leaves than the ones in the pictures though. Probably lots of variations available.
 
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