indentify volunteer flower?

Can anyone I.D. this plant that appeared in our woodland garden in central North Carolina?
http://nickplummer.home.att.net/unk2.jpg -- Flowers
http://nickplummer.home.att.net/unk3.jpg -- leaf
The plant produced a rosette of leaves last year, vanished during the winter, and reappeared with a 3-4 foot stem this year. It gets some sun around mid-day but is otherwise shaded by mature deciduous trees. I have no idea whether it is a wildflower or an escaped garden variety.
I suspect it might be a Campanula or something similar, but I can't find anything that matches exactly.
Thanks.
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Looks loke Campanula rapunculoides
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It looks like campanula rampunculoides to me too. If that is the case, ERADICATE ERADICATE ERADICATE! Its nickname is "cancer of the garden", because it spreads from the tiniest fragment of root when you attempt to pull it up. The main root is a long white root, something like a small parsnip - but it will send out long exploratory fibrous roots in any direction to shoot up another stalk.

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Thanks for the information. Most of the photos I found of C. rapunculoides showed leaves with much smaller "teeth" than our plant. Is that a variable trait? If it is C. rapunculoides, I'll certainly try to eradicate it. I wouldn't want it to choke out the Tipularia discolor and Stylophorum diphyllum
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I just looked at some more pics of Campanula rapunculoides. They all show a plant with flowers widely spaced on a long terminal inflorescence. My plant has flowers in clusters at the leaf axils along the length of the stem.
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