A few people have asked me about this plant recently. It’s called a ground plum in English. Ptétȟawote, or Astragalus crassicarpus.
I believe that the fruit is technically edible, though it was pretty bitter and woody when I tried a ripe one about 4 summers ago at the site of Sacred Stone Camp. The fruit has a cucumber-like texture, but isn’t sweet. I wouldn’t recommend eating it. We seem to be having a bumper crop this year.
I don’t know much about traditional uses of this plant, but the name translates to “buffalo food.”