About Harpagophytum procumbens (Burch.) DC. ex Meisn.
Harpagophytum (pronounced HAR-pə-GOF-it-əm), commonly known as devil's claw, and also called grapple plant and wood spider, is a genus of plants in the sesame family that is native to southern Africa. The genus gets its common name devil's claw from the unusual hooked shape of its fruit. Note that several North American species in the genus Proboscidea and some Pisonia species are also called devil's claw. The tuberous roots of devil's claw are used in folk medicine to reduce pain. Harpagophytum procumbens is mainly found in eastern and southeastern Namibia, southern Botswana, and the Kalahari region of the Northern Cape, South Africa. H. zeyheri occurs in northern Namibia (Ovamboland) and southern Angola. Harpagophytum procumbens grows in deep, sandy soils in areas with low annual rainfall between 150 and 300 mm per year. It is a perennial, tuberous plant that produces new creeping stems each year. Above-ground stems sprout after the first rains, and die back during droughts or after frosts. Stems grow from a long-lasting primary tuber; the harvested parts of the plant are secondary tubers that grow from the primary tuber at the end of fleshy roots. The plant gets both its scientific and common names from the hooked spines on its woody capsules. Mature fruit opens slowly, so only 20 to 25% of a plant's seeds may come into contact with soil in a single year. Seeds have a high level of dormancy, a low respiration rate, and can remain viable in the soil seed bank for more than 20 years. The sustainability of the international devil's claw trade has been a topic of concern for many years. The governments of the three range countries where the plant grows—Namibia, Botswana, and South Africa—have created policies and regulations to protect the species, set sustainable harvest limits, and support continued livelihoods for harvesters. Proposals have been made at different times to list the species for protection under the Convention of International Trade in Endangered Species (CITES), but these proposals were withdrawn after the range states implemented sustainable trade management measures. Multiple studies have investigated the biological and ecological needs of both harvested and unharvested devil's claw populations. Early short-term studies in Botswana looked at the species' ecological requirements, while more recent work has surveyed the resource and studied sustainable harvesting methods. Understanding the ecological requirements of a harvested species is necessary to manage harvest to maintain sustainability. Stewart and Cole (2005) studied the complex economic, social, and cultural factors connected to devil's claw harvest. Stewart (2009) assessed population structure, density, growth, mortality, and seed and fruit production in harvested and unharvested populations in the Kalahari savannas of South Africa. Plant density and population structure differed significantly between overgrazed areas and grass-dominated areas, which suggests the variation may stem from competition for limited water and nutrients. Experimental harvest via removal of secondary tubers did not cause significant mortality in any of the harvested size classes. Harvest also did not impact overall growth, though medium-sized plants grew more over the study period in both harvested and unharvested populations. Fruit production was highly variable, and mature fruits only developed under favorable conditions. Under the conditions of this experimental harvest, the species appears resilient to harvest; harvested plants survived at the same rate as unharvested plants. However, because of the spatial variation in the species' habitat and the phenotypic plasticity of the plants themselves, more harvest data from large numbers of plants in actual harvested areas is needed to better understand the species' full life history. Ethnobotanical use of devil's claw originated in southern Africa. H. procumbens is one of the floral emblems of Botswana, where it is believed useful for treating a range of pain conditions. Preparations made from the plant or its extracts, including the compound harpagoside, are used as an anti-inflammatory herbal drug or dietary supplement in folk medicine and phytotherapy. There is no universally accepted clinical evidence of devil's claw's efficacy and bioavailability, but limited effects have been observed for treating lower back pain and osteoarthritis. A 2016 Cochrane review of clinical research found that devil's claw appears to reduce low back pain more effectively than placebo, though the evidence was only of moderate quality at best. As of 2022, further research into the plant's effects on pain and inflammation is considered worthwhile.
