Hello,

I'm fairly sure that your mystery plant is silverleaf nightshade. (Poisonous!)

Lindsey :)

Thanks Lindsey!

Yup that's what it is - it's extremely difficult to get rid of - much like bindweed in it's rooting habits - deep and makes new plants from broken roots. It's also covered in needle sharp hairs - they go through double thickness leather gloves like nothing was there.
I hate 'em...

lol that plant i see in my back yard well used to i tilled all the dirt in back gonna plant some real grass cause i used to have that crappy grass that grows anywhere and that little purple flower i just recognined i hate them once i tried to pull them out and boy was that a bad idea....:-P as abq bob has said those suckers hurt...the poison but oh well so much for them they are gone and the roots and all is dried up....tiller do miracles :-P

I like those things! I have had one in my backyard for quite a few years - I didn't know what it was either. I think they're pretty!