Jimsonweed. I notice that it is growing next to a pile of soil. The seeds might have come in with it.

Ding-ding-ding-ding!!! I think we have a winner! :-) Specifically, I believe it's Solanum carolinense f. albiflorum - http://www.missouriplants.com/Whitealt/Solanum_carolinense_page.html states the regular carolinense has the lilac blooms which threw me off the horse nettle trail when I saw it earlier (didn't check the missouriplants.com page at the time, now I know where to start looking, don't I?). Thanks so much for pinning it down for me, farmerdell. Yep, those were nasty spines; thankfully I was out pulling thistle and was somewhat protected. We will have to do something more than pull it up; I noted at the time that no roots came up, it was just breaking off... was rushed at the time and had a lot of weeding to do so figured we would carefully take brush killer to it when it comes back up. Thanks again so much, everybody!

I also thought that but didn't come up with anything. I thought Sida....

The leaves are fragrant, like a lemony scent. I couldnt find the flowers anymore.