Comfrey, Symphytum officinale. Here is a link that might be useful: Comfrey images

Thanks! I do agree that it is Bidens - apparently there is Bidens alba (which is native) and Bidens pilosa (which is introduced). Both are rather weedy! Looking at pictures, it seems this one is Bidens alba. I do think I'll dead head this plant as it finishes flowering; apparently it is very popular with butterflies so it would be nice to leave it for them but avoid having the seeds for next year.

I think what I thought was milkweed syriaca (sp) is actually dogbane. I have a growing stand of it way in the back that I've let go for the past two years. It showed up on its own, and if it is dogbane, I'm going to yank it, dig it, destroy it this year. I'm trying to remember what the seed heads looked like, but I'm drawing a blank. I do remember getting the tent caterpillars on them last year, and I've read the dogbanes will get those. So, in answer to your question, that's the only experience I've had with it, and I don't want it to continue. LOL.

Well, they don't exactly explode. You will come out one day and the opening process will have begun. The bolls fluff out gradually. Then....mail me the seeds. How amazing that you have a cotton plant volunteer.