Friday, August 8, 2008

Carduus acanthoides

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.


Justin said...

Never seen it. I have seen Carduus crispus in Wisconsin, which has smaller heads and has more developed winged tissue on the stem. Seems like it should have been found in IN, given it greater distribution. Eventhough it is a weed, it is a sweet find. The more we know, right? Nice work, Scott!

Brad said...

Interesting find, Scott. This summer has been my first significant introduction to Carduus nutans, which is locally abundant in southeastern Michigan, where it occurs in old fields, fencerows, and pastures. These thistles are fascinating yet hideous.

Scott said...

I considered Carduus crispus as well. I've never seen this one either. I think the size of the involucre separates C. acanthoides from C. crispus.

Scott said...

Not sure if anyone looks at these older blogs or not. I've had a couple of people ask me recently if this could be Cirsium vulgare. I think the only way to tell Cirsium from Carduus is the pappus (which consists of plumose bristles in Cirsium and capillary bristles in Carduus). Regardless of that, this plant looked nothing like Cirsium vulgare in the field, and I still don't think it does in these photos. Anyone have any thoughts? I'll have to wait until next summer to collect this and verify that it is indeed a state record, as it's 2 hours away from my house.