FOREST ELEPHANT’S FOOT - Dioscorea sylvatica
The multiple trailing vines from the tuber can cover large areas with beautiful heart-shaped leaves which become deciduous in frosty, exposed places but remain all year in protected environments
The plant genus, Dioscorea, is named after the Greek physician, pharmacologist and botanist Pedanius Dioscorides (40 - 90 AD) probably due to its value in medicine and cuisine. The genus is best known for the swollen tubers, or yams, it produces which are a valuable food source in the moist tropics in the Americas, Africa and Asia and has been cultivated for 10 000 years. The inability to mechanise the very laborious harvesting process is probably the only reason it is not more widely cultivated. But even with this difficulty in harvesting, a recorded 73 million tonnes of yam was harvested in 2017 worldwide with 95% of that being in Africa and 66% in Nigeria alone.
The species of Dioscorea that concerns us here in MACNR, is D. sylvatica ( from Latin -from the woods / forest). By far, the largest part of the plant is contained in its massive, swollen tuber which is, of course, entirely or partially covered by the soil so not so easy to spot. But the climbing vines grow from the tuber in all directions and can reach lengths of 5 or more meters in a growing season, filled with striking heart-shaped leaves. When in bloom, the flowers, whose male and female adorn different plants, hang in pale strings that contrast with the dark green leaves to provide a beautiful display in the shade of the forest.
The pale greenish yellow flowers hang in strings in the dappled shade of the forested gorges in the reserve. These are male flowers.
Now this is the story: The Forest Elephant’s Foot was a rather common plant here in Mpumalanga and the rest of the eastern portion of Southern Africa before it was discovered, circa 1950s, that the tuber contained high concentrations of diosgenin, a substance that could be processed to produce Cortisone and other steroid hormones. The demand for the tuber grew rapidly and the wild harvesting of the entire plant, which is necessary to obtain the tuber, accelerated dramatically. By 1955, the government attempted to restrict the harvesting by introducing a permit system, only allowing harvesting on privately owned land and not government conservation land, and restricting tuber size to greater than 300mm in diameter. This was difficult to police and between 1955 and the end of 1958, 3 466 tonnes of the tubers were wild harvested in the former Transvaal alone and by 1960 wild harvesting was no longer viable because of the severely depleted wild populations. During this time many attempts were made to cultivate the plant but it was soon established that it was too slow growing (1x Forest Elephant’s Foot generation = 30 years). Subsequently, the use of the plant for Cortisone production was abandoned.
Although the Forest Elephant’s Foot is a monocotyledon like grasses and sedges,the leaves, unusually, have net-veins like a dicotyledon.
In 1999, the South African National Biodiversity Institute (National Botanical Institute then) declared the plant “Lower Risk - Near Threatened” but that was reevaluated to “VU A2cd” a decade later because it seemed the populations were still in decline. The International Union for Conservation of Nature (IUCN) established its Red List in 1964 and the above classification of a plant means: Vulnerable; A2 - Population reduction observed, estimated, inferred,or suspected in the past where the causes of the reduction may not have ceased or may not be understood OR may not be reversible; c - A decline in area of occupancy, extent of occurrence and / or habitat quality; d - actual or potential levels of exploitation.
This is quite serious.
More than 16 tonnes a year pass through traditional muthi markets, in KwaZulu Natal alone, where sangomas use it to treat epilepsy, hysteria, insomnia and acute psychosis. The current demand for the tubers in traditional medicine together with its history of over-exploitation and its long generational time are making it difficult for the plant to reestablish itself in sufficient numbers in the wild.
The three-winged seed pods are easy to identify as strings of seeds under the forest canopy.
The Mpumalanga Tourism and Parks Agency, together with SANBI, are in the process of drawing up a provincial management plan for this and 5 other species of plant and have asked local stakeholders and interested parties to report sightings and locations of plants to help them map current populations for this plan.
After receiving this request from SANBI, I browsed through my “Unsolved” file and found photos of two individual plants that I had photographed and not been able to identify in the past. I checked my diary to see where I was when I photographed these plants and one was in February this year while I was walking in Slit Gorge, just north of Pebble Creek (unit 25), with the new family, The Andersons from Kingfisher Lodge. And the other was when I was preparing the ignition tracer for a patch burn last year which would put the plant in the gorge above the Mountain Hatchery. Then, more recently, in May, I found a plant adorned with seed pods on Mount Prospect 159JT while inspecting the work of the MTPA alien clearing teams.
All these sightings, in steep, wooded gorges, are quite far apart and this would suggest that we may have more of these plants in our reserve. The more we involve ourselves in conservation efforts, the more important this area becomes for plant conservation. So please, keep your eyes out for these unique vine creepers and if you find one, try to photograph it and record its location or contact me and describe where you found it. I will pass the details on to MTPA and SANBI.
