Name: Christine North East Texas (Zone 7b) Shine Your Light!
First time finding this plant at the pond's edge. I thought it might be Ludwigia peruviana but the stem doesn't seem to match. The plants stand about 4 ft high and are trailing along west bank of the pond.
Ribbed stems
May your life be like a wildflower, growing freely in the beauty and joy of each day --Native American Proverb
I did look at L. octovalvis and a couple of others. I'll give it another look. 
