Genetic, morphological and chemical variation in the genus Harpagophytum

Abstract: Harpagophytum procumbens is a valuable medicinal plant but mistakes with plant identification at harvesting, and wilful adulteration using the presumably less efficient H. zeyheri are suggested. A multidisciplinary study with plant material from Botswana was conducted. (1) Morphometric measurements on seed capsules showed continuous variation between and, in some cases, within locations indicating occurrence of interspecific hybridization. (2) Mitotic and meiotic chromosome counts, that need to be ascertained, suggest 2n=20, 20/22 and 24 in the studied materials. Meiosis in a putative hybrid appeared regular but occurrence of dyads and triads at the tetrad stage indicated disturbances. (3) DNA markers for seedlings from field-collected seed capsules suggest that outcrossing is prevalent. While the two species showed significant differentiation, some morphologically deviating plants had intermediate DNA profiles possibly representing introgression products. (4) Analysis of selected biochemical compounds in peel and pulp of the tubers showed that content of the main bioactive compound harpagoside was significantly higher in H. procumbens compared to putative hybrids and H. zeyheri. In both peel and pulp, contents of isoverbascoside, verbascoside, acetylacteoside and pagoside were higher in H. procumbens and putative hybrids compared to H. zeyheri. (5) Tuber extracts were investigated for antioxidant capacity, content of total phenols, important phenylpropanoids and selected iridoids, and capacity to suppress respiratory burst in terms of reactive oxygen species produced by human neutrophils challenged with phorbol myristate acetate, opsonized Staphylococcus aureus and Fusobacterium nucleatum. A new variety of H. procumbens ssp. transvaalense showed the highest degree of antioxidative capacity, wheras an anti-inflammatory effect could not be corroborated for any of the tested extracts.