This is the spot where I planted camomile, but I'm pretty sure that's not camomile... Unless I'm totally crazy. Help?!
Definitely isn't Chamomile. Not enough detail to say for sure, but it looks somewhat like a tomato. edit: I was finally able to enlarge the photo and it's not a tomato. Yes, it appears to be a Mustard.
It's definitely from the brassica family, probably wild cabbage or maybe a seedling from a crop left to go to seed, in which case it could be showing traits of a number of different parents.