Something from the Mustard family. Although I've never seen it in person, your plant bears a resemblance to the dreaded Garlic Mustard that folks out East are fighting...

Mike

Mike is right, that's Garlic Mustard, a terrible pest that spreads everywhere and chokes out native plants. You can confirm it by the odor of the bruised leaves, they smell like garlic.

It's a biennial, so the plant in your pic grew from seed last year, survived over winter, and will set seed and then die this year. But the seeds remain viable for 5 years, so if you can pull it up before the seeds ripen you will have that much less weeding to do for the next 5 years, lol.

Also you can help prevent further spreading by pulling up the first-year seedlings so they don't get a chance to bloom and set seed next year. The leaves on the young seedlings are more rounded and don't have the sharp-toothed triangular shape of the ones on the flower stalk in the pic.

Here is a link that might be useful: {{gwi:1344065}}

Oh My God - it's Garlic Mustard - kill it now, kill it good - or you could end up with this!

{{gwi:1057711}}

OH MY GOD, Upstate!!it's an emergency. Well, I'm glad that I asked because I have always thought this was jewelweed, and never knew what a bad thing I had! And I am in NY, too, and never heard about this problem, geeze.

I have clumps of it, not fields(yet) so i went out and pulled what I could. Will dumping a thick layer of mulch on the area kill it eventually.

Thanks everybody.

Anita - I know, it's a nightmare - I was so busy for 3 yrs digging up Jerusalem artichoke that I didn't pay attention to the woodland part of our yard, and now THIS!! From what I understand, the seeds can live for 5 yrs in the ground, so try to get them all before they drop their seeds. I've filled 5 huge lawm bags full of this stuff so far - plan on keeping at it all summer - then Round-up in the fall after everthing else has died back, then again in the spring! I imagine this will go on for a few years until I get a handle on it!

It is all over illinois also- especially under trees in wooded areas