Anybody recognize this? It sprang up in an abandoned pot in my backyard and I've been letting it grow to see what it is - something leguminous? Flowers are small - I put my hand in the pic to show size - maybe 1/2 inch or 10-12 mm. Plant is maybe 3 feet/ 1 meter tall right now.

I sometimes tuck the odd seed in pots like that and then forget I did it, which might be the case here.