Looks like a GLORIOUS well-fed weed about to share a multitude of seeds with your garden area.

Many who has sown lots of unfamiliar seeds or has inherited another gardener's garden has done the same, tending and nurturing an unknown plant that rewards them with stubbornly refusing to leave after the welcome wagon ends and all care stops. My 'perennial poppy' ended up being a vicious thistle that had knotted brittle horizontal roots, and it plaques me in my perennial bed to this day.

Somebody said it's an annual mercury, used in the past for medicinal purposes but considered a weed nowadays. As glorious as it look I think you're right about the seeds spreading. Saying that though if that's what happened in the first place I wonder why we've only got one? Perhaps I managed to pull them up before they grew. We're in the middle of a storm for the next few days so I think I'll give it a reprieve for a while, thanks.

It only takes one seed to grow a giant weed, but the next season is when you'll have to be vigilant with new seedlings.

Quick- get ready to plant TONS of dahlias so they will shade out the weed seedlings! Works for me!

Good idea! The weather was better today so I threw it out. Tomorrow it's back to picking all the small ones out again and again and again.....

Thanks for all your comments everyone. Will try harder!