Help ID this pretty white flower???

I have asked the folks in the ID forum, but I thought I would ask our Butterfly enthusiasts too if you can ID the little white flower behind the iris? It is soft and airy, fuzzy and about 2 or 2 1/2 feet tall. Lance shaped leaves. And it blooms early on with the early tall-bearded iris. (It is not like the gypsophilia that I also have in the garden.)

Unfortunately, this is the best pic I have of it. I went through several seed catalogs, and looked around on the internet, but could come up with nothing. I don't know where it came from (I have wintersowed seeds like crazy, but went through my seed list and didn't see anything matching).

I thought maybe the seed came from one of the butterfly gardeners on DG and you might recognize it? I thought it might be related to wild ageratums?....It's almost a weed, but a very pretty 'filler' for the early spring garden...

Any leads would be helpful. Thanks. t.

T - I can't make out the flowers/plants at all from the photo. Any chance of cropping and making the photo bigger? Sorry.

I took these pics this morning--a few stragglers leftover from my garden clean-up this week....

(not very good pics, either)...

Another (bad) close-up, but maybe it will help. Sorry.

Thanks everybody--

I think that Patrick IDed it as Corn Salad--- a weedy flower that is not much in cultivation except for some herb/salad uses...

http://davesgarden.com/pf/showimage/73788/

I don't know if the butterflies like it or not, but it was a very nice little filler in the garden this spring.