Devil's claw is the common name for two species in the genus Harpagophytum. Their root extracts contain the iridoid glycoside, harpagoside, which has been found to be effective in the treatment of degenerative rheumatoid arthritis, osteoarthritis, tendonitis, kidney inflammation, and heart disease. Most of the world's supply comes from Namibia, with lesser amounts from South Africa and Botswana. In 2002, the peak year of export, 1018 tonnes of dried tubers were exported from southern Africa, representing the harvest of millions of plants. In 2001, sales in Germany were estimated at 30 M euros, accounting for 74% of the prescriptions for rheumatism. Harvest has improved income levels in marginalized communities but it has also raised questions of sustainability.