I submitted photos in August of a mystery plant, and you suggested Sesbania as an ID, but it did eventually flower in October, and I wonder if the plant could be Aeschynomene americana?
The curved seed pods were charmingly scalloped, segmented and a bit fuzzy—I think you can see one in the 2nd photo.
Thanks for your help,
I think you are correct and that it is Aeschynomene americana. It is certainly not Sesbania. There seem to be two other species of Aeschynomene to be considered, Aeschynomene indica and Aeschynomene virginica. Aeschynomene virginica is a federally listed species and not known in South Carolina – it is found north of us. Aeschynomene indica is an introduced species found in disturbed areas and is well known to be in South Carolina. However, Aeschynomene americana has not been reported in South Carolina as far as I know. It is well known in Georgia, Florida and a few other states. You might check with the herbarium in Columbia at the University to see if they have any records. Yours may be a new record. The flowers and leaves do seem to match Aeschynomene americana very well. See: https://www.wildflower.org/plants/result.php?id_plant=AEAM
I hope this helps. Nice pictures!
Dr. Steven Hill, Botanist, SCNPS