Does anyone know what this plant is that popped up in my garden?

Looks like a weed although I cannot identify it.

I don't know what it is , but it looks like a weed to me. If you don't want to pull it yet then leave it but don't let it bloom and then drop seeds if you also decide it is a weed. Weeds are voracious eaters and will deplete the soil. Take heed there is truth in the old saying, "One year seed, seven year weed."

Looks like a weed to me. I live in Maine and have never seen a flower like this.

There's a terrific app for smartphones called garden answers plant identifier. You open the app, take a photo and it gives you suggestions to help you identify it.

is it sticky to touch? I could be what I know as matress weed.

It is a weed and very invasive.

Pull it out from the roots and make sure that it does not come back.

I have had it on and off in England (UK) in my garden in Suffolk

Looks to me like asparagus fern, which has nasty thorns, and is invasive!!

It is in the fern family 'asparagus fern'....take a sample to nursery where they carry plants.....that's what it looks like to me.......

Thanks everyone for your help. I'm in the trimming and digging out mood for this weekend and can't wait to start loading our little trailer and making the yard beautiful!!!