Chelidonium majus is a European plant which has naturalized in much of our continent, including MN. Stylophorum diphyllum is native to eastern North America, but does not occur naturally in MN according to the USDA Plants Database. I didn't put that in as a link because the service went down right after I checked it. http://plants.usda.gov/index.html is the home page--good place to start on researching any plant, IMO.

So neither is native to your state, even though the "most foreign" may be found growing in the wild.

If you want more info on differentiating them, the Styllophorum has a hanging oval, furry seedpod (very cute) while that of the Chelidonium is long and skinny. I understand the Chelidonium is a very heavy seeder, and obviously invasive. I grow the Styllophorum, so I know from experience it is quite a prolific seeder also. However, I don't find it to be "pushy," it just takes over when it finds a bare spot. Perhaps it is too cold for it up there and that is why it does not occur naturally.

Here is a link that might be useful: Styllophorum page on IllinoisWildflowers

They are a little tricky to tell apart at first. The flowers of the Native (Stylophorum) are decidedly more poppy like. The easiest way to tell them apart, as dbs_illinois suggests, is the seed pod. Now that I know them a little better, I can almost tell from the leaves

a previous post:
Garden Web: celandine native (stylophorum) and alien (chelidonium)
since this post, I've been pulling the introduced Chelidonium majus out and encouraging the native.

USDA Chelidonium majus

Here is a link that might be useful: usda - Stylophorum diphyllum