Abstract
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: Harpagophytum procumbens and H. zeyheri. Although the European pharmacopeia considers the species interchangeable, recent studies have demonstrated that H. procumbens and H. zeyheri are chemically distinct and should not be treated as the same species. Further, the sale of H. zeyheri as an herbal supplement is not legal in the United States. Four markers were tested for their ability to distinguish H. procumbens from H. zeyheri: rbcL, matK, nrITS2, and psbA-trnH. Of these, only psbA-trnH was successful. A novel DNA mini-barcode assay that produces a 178-base amplicon in Harpagophytum (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: H. procumbens was not detected in 75%; 25% contained both H. procumbens and H. zeyheri; none contained only H. procumbens. We recommend this novel mini-barcode region as a standard method of quality control in the manufacture of devil’s claw supplements.
Highlights
Harpagophytum (Pedaliaceae) is a genus of tuberous plants from the Kalahari Desert and Namibia Steppes that is commonly known as devil’s claw due to its hooked fruits [1].The genus comprises two distinct species—H. procumbens and H. zeyheri—that have been separated on the basis of morphology [2,3,4] and chemistry [5]
Among the 20 fully-analyzable supplements: H. procumbens was not detected in 75%; 25% contained both H. procumbens and H. zeyheri; none contained only H. procumbens
Harpagophytum zeyheri comprises three subspecies [3], H. zeyheri subsp. zeyheri, which is restricted in distribution to northeastern South Africa, and H. zeyheri subsp. schijffii and H. zeyheri subsp. sublobatum, which are both widely distributed across regions of Angola, Zambia, and Zimbabwe and the northern regions of Namibia and Botswana
Summary
Harpagophytum (Pedaliaceae) is a genus of tuberous plants from the Kalahari Desert and Namibia Steppes that is commonly known as devil’s claw due to its hooked fruits [1].The genus comprises two distinct species—H. procumbens and H. zeyheri—that have been separated on the basis of morphology [2,3,4] and chemistry [5]. Botswana, and Northern South Africa, and H. procumbens subsp. Harpagophytum zeyheri comprises three subspecies [3], H. zeyheri subsp. Zeyheri, which is restricted in distribution to northeastern South Africa, and H. zeyheri subsp. There are unsubstantiated reports of possible hybridization in the few places where. Purporting to demonstrate hybridization, RAPD and ISSR data [7] are, at best, inconclusive: no species-specific genotype groups were detected [7], a definitive pattern of hybridization cannot possibly be observed; the published Principal Component Analysis [7]—which is inappropriate for detecting hybridization [8,9]—identifies five putative hybrids, but only one individual is truly intermediate while several non-hybrid samples are or more intermediate than the putative hybrids; and the published UPGMA dendrogram [7] refutes the hypothesis of hybridization because it nests the putative hybrids well within the two parental clusters rather than at the cluster base where hybrids are expected to appear [10]
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