I live in West, Central Illinois. We have moderately clay-y soil (grey, not red). We recently moved to a house in the country and there are a TON of plants in our yard that start off kind of like rhubarb (red stalk, broad, somewhat crinkly (curly) leaves and proliferous.
However, the stalks are not rhubarb-like in that they are not cupped along the length. Also, as they get taller, there are more leaves up the stem, unlike rhubarb. And they don't spread laterally in the way that burdock is said to do. They are often near 4 feet tall and not near that wide at the base. They are rather woody and the root is layered (like a beet or turnip), but not wide or bulbous and very large and hard to find the end of. The thing that's throwing me off here is that all the descriptions I've read and pictures I've looked at for burdock show cupped stems and stalks and these poky purple flowers on top. The stems on these are smooth and I have not seen any flowers or burrs as ascribed to the burdock.
No matter what it is, I want it out of my yard (I pulled 20 or more out of a 4x4 space in one corner of the fence), but it's driving me crazy in not being able to identify it! I have also observed it on the edges of the woods that run along the creek.
I wish I had a picture right now. If I remember, I'll post one.