Since a major gall stone attack about 10 years ago, every summer my family collects Joe Pye Weed (Gravel Root) and makes green drink from it as well as drying some for winter usage. Now if I get a tell-tale twinge, I start taking apple juice to soften the stones and have a glass of gravel root tea each day for a few days to dissolve them. It works every time. I'm not even aware when they pass. (I also try to do the kidney-gall bladder flush each fall.)
In addition, we collect the gravel root each August and feed it to our dairy goats. We lost a buck about 15 years ago to kidney stones. Haven't had a case since. Also, a friend cleared up his kidney stones and has had no more. He was seeing a doctor every few months and was told he would have to for the rest of his life. Now he drinks a glass or two a week of the tea and has had no trouble for 2-3 years plus his general health has improved.
All parts of the plant are useful, but we don't mess with the roots because they are a pain to clean. We collect the plants from along creeks and country roadsides when their flowers are their brightest pink. (They are truly pink, NOT purplish. ) The following website has a good picture of the plant although the color is somewhat washed out. The flower head can be very conical. I suspect it is forming seeds: www.altnature.com/gallery/joe_pye_weed.htm.