Look up baptisia species.

Could it be
Astragalus canadensis (Canadian milkvetch)

Are you sure it was on a 'prairie'?

I can think of a few bad spp that I would not like to transfer that are a 'bean pod with seeds' in waste areas of Wisconsin. You can always seedling flat them out before you spread them to see what comes up this winter indoors.

Astragalus has a lumpy, large seedbody and Baptisia has ~ the same shape/size of a soybean. My guess is its crown or cow vetch.

Froggy

Thanks for the suggestions, but the pods do not look like crown vetch, my baptisia or other pea-shaped pods. They are dark brown, slightly pointed sausage-shaped, stiffly upright in a small cluster at the top of the stem. The seeds have mostly been eaten but I found enough to plant for spring growing to see what comes up but thought the description might ring a bell with someone. There are a number of these plants on this planted prairie so I can't prove whether they are just weeds (although I didn't see any elsewhere).