"Fast Growing" unknown Plant or Tree?

This odd little plant sprouted from mulch (I think) and for the life of me...I have no idea what it is. I've ruled out any sort of Mimosa or Pride of Barbados....since the flowers are tiny, yellow and attached to the stem. Or would I call it a trunk at this point? Its been too dadgum hot around here to even take a photo down to my favorite nursery (Rainbow Gardens.) The blooms actually sort of look like sweetpeas and this "thing" is growing about an inch a day! I swear! Well...its a fast grower, anyway...lol. Anyone care to take a guess? Oh and it has soft thorns on the trunk as well...

Partridge pea:
http://davesgarden.com/pf/go/51669/index.html

Debbie

Hmmm....the blooms and leaves look similar to the partridge pea, dmj1218, but the flowers on my strange plant are only blooming on the stalk. They last for a few hours and then fold up again. The trunk is sort of soft too...as if it is almost hollow. The leaves are thick and heavy.

don't know what it is, just commenting that reminds me of a mimosa, or something in that family.

Could it be this one?

http://aggiehorticulture.tamu.edu/ornamentals/nativeshrubs/caesalpiniawooton.htm

Josephine.

Sorry--just a guess..I always pull 'em.

Hey, welcome to DG, TxTurqoize!! It's a great place to hang out!
CJ

It looks like either Sesbania herbacea or Sesbania drummondii. The leaves on both are alternate and contain 20 - 50 leaflets each. S. herbacea is an annual. The leaflet tips are rounder and lack that small pointed peak at the end of the leaflets. S. drummondii is an herbaceous short lived perennial. If it is a Sesbania, you will be able to identify the species by letting the seed pods develop long enough to differentiate between the two species. This website has photos of the different seed pods.
http://www.sbs.utexas.edu/mbierner/bio406d/PlantPics_archive.htm

In any case, Sesbania tends to spread like wildfire. You may want to remove the seed pods before they mature if you don't want more plants. If you have pets, don't let them eat the seedpods as they are poisonous.

Veronica