| Summary: | Devil’s claw is the vernacular name for a genus of medicinal plants that occur in the Kalahari Desert and Namibia Steppes. The genus comprises two distinct species: <i>Harpagophytum procumbens</i> and <i>H. zeyheri</i>. Although the European pharmacopeia considers the species interchangeable, recent studies have demonstrated that <i>H. procumbens</i> and <i>H. zeyheri</i> are chemically distinct and should not be treated as the same species. Further, the sale of <i>H. zeyheri</i> as an herbal supplement is not legal in the United States. Four markers were tested for their ability to distinguish <i>H. procumbens</i> from <i>H. zeyheri</i>: <i>rbcL</i>, <i>matK</i>, nrITS2, and <i>psbA-trnH</i>. Of these, only <i>psbA-trnH</i> was successful. A novel DNA mini-barcode assay that produces a 178-base amplicon in <i>Harpagophytum</i> (specificity = 1.00 [95% confidence interval = 0.80–1.00]; sensitivity = 1.00 [95% confidence interval = 0.75–1.00]) was used to estimate mislabeling frequency in a sample of 23 devil’s claw supplements purchased in the United States. PCR amplification failed in 13% of cases. Among the 20 fully-analyzable supplements: <i>H. procumbens</i> was not detected in 75%; 25% contained both <i>H. procumbens</i> and <i>H. zeyheri</i>; none contained only <i>H. procumbens</i>. We recommend this novel mini-barcode region as a standard method of quality control in the manufacture of devil’s claw supplements.
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