Hmmm, wild mustard doesn't seem to help. I can't find any references to it other than garlic mustard, which it definately is not. Garlic mustard would make me happy cause it's yummy! Thanks tho!
I don't remember the flower it produced, but it is a lot more feathery than pineapple weed leaves. More like dill than a fern. The pineapple weed looks like it has leaves kinda like lavender.
The white stems are fairly fragile and the leaves are very soft, not at all prickly. It either reseeds where it is, or it comes back from the roots, as I can see old stems from last year's plants all around the base of this seasons growth.