Stinging Nettle
It's a bush like plant that has several medicinal qualities and relieving arthritis pain/swelling is one of them.
I remember one comical, anecdotal story of some people who were walking in the countryside when a random guy walked past them and straight into a patch of stinging nettle, then commenced to wallowing around in it. I can image the looks on their faces, but the guy later explained the reason for his action. Not that diving into stinging nettle is advisable, but maybe pain replacement was what the guy was after. I believe most people grab a handful and rub it on the affected site.
The story of three wheels and a man...