While in northeast Indiana this week, I might have stumbled upon a new state record. Below are photos of what I believe to be Carduus acanthoides, spiny plumeless thistle. This species is native to Europe but a noxious weed on several other continents.
You'll notice that it looks quite similar to the Onopordum acanthium that Keith posted a few weeks ago. In fact, that's what I thought it was when I saw and took photos of it. Like Onopordum acanthium, this plant has a spiny, winged stem.
Upon closer examination, though, I noticed that this plant has a chaffy receptacle, which Onopordum doesn't have. Also, you'll notice that the involucre is a different shape than that of Onopordum.
I've sent photos to Mike Homoya and Kay Yatskievych to get their opinions, and to find out if Carduus acanthoides has been found in Indiana before. It's shown as occurring in all of the surrounding states.
I'm interested to hear any of your thoughts on this.