Ludwigia species- Sonepat, Haryana
Growing along an irrigation channel.
Sonepat, Haryana, today (23.10.09)

This represents Ludwigia sp.

As ... identified, it is Ludwigia.
If the stamens are 4 and the fruits 4-ribbed, it is L. perennis.
Whereas, L. hyssopifolia has got 8 stamens and the capsules are 8-ribbed.
Locally called as 'kaattu kirambu' in Tamil meaning 'wild clove'