Can any one identify this plant?

[mcp]

This plant sprang up in my pot of Arrowhead. I believe it is just a weed. I just let it grow as I was curious to see what kind of flowers had on it. Thought they were kind of unique. Can anyone tell me what the name of it is? Thanks in advance.

[Joyce]

Look like Lizard's Tail to me.
(Saururus cernuus)
Quite invasive if let loose, basically a weed. 

How big is it?
If it's over 2 feet tall, it could be Japanese Knotweed.
(Fallopia japonica, syn. Polygonum cuspidatum, Reynoutria japonica)
Horribly invasive. Worse than a weed. 

Both plants are in the same family.

[ponderer]

Looks like Lizards Tail . Scented flowers?

[pixiedust]

Looks like lizards tail to me too

[tweetybaby2005]

I have one just like yours and when I bought it, it was labelled as Lizard's Tail.

Kuan

[bunny56lbc]

Look's like Lizards tail to me too .

bonnie

[perplexed ponder]

I believe it is gooseneck loostrife...check out this link

http://davesgarden.com/guides/pf/go/656/

[Celia]

Interesting, I had a plant/weed just like it come up on its own.  I said it had to be weed because wasn't planted, but DH said plant.,  we also just let ours grow. 

[matherfish]

The top left stem bloom looks like a Lizard's tail bloom stalk from the picture. I agree with those who say it is a lizard's tail.

[mcp]

Thanks for all the advice on the name of plant. I think I will go with the consensous and believe it is Lizards Tail. Have no ideawhere came from. I think I will just pull out and disgard unless some one wants for postage. Thanks again.

[miguynmkoi]

I had a plant like that growing in a corner of my front yard.  I didn't put it there and after a few hours of weeding last week I decided to pull it out.  I'm glad I did.  After reading here that it is an invasive weed....phew weeeee!