At first I thought it is a viola. Violas (johnny jump-ups, hearts-ease) can get leggy -- they tend to flop over when they get too tall. However, a closer look makes me think it's torenia, although the foliage isn't quite the same as on mine.

Something in the Apiaceae. I'm not familiar with Carol23's suggestion but it looks a possibility from images.

Seems there are many that look like this, but Hackberry comes to mind. I treated it as a weed tree on my acres, but it is persistent.

GW has a plant identification forum. Name That Plant!. I am not familiar with it so cannot attest to its usefulness.