Dioscorea elephantipes
| Light | Bright light to gentle direct sun; more shade while the vine is growing |
|---|---|
| Water | Water while in active leaf; keep dry during dormancy (see Watering) |
| Soil | Very free-draining, gritty mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; USDA zones 9b–11 |
| Propagation | Seed (see Propagation — seed) |
| Toxicity | Contains bitter saponins; the raw plant is regarded as toxic if eaten — keep away from curious pets |
Dioscorea elephantipes is a slow-growing, caudiciform yam from the arid interior of South Africa, grown almost entirely for its extraordinary swollen stem base, or caudex. Over many years this woody caudex develops thick, corky plates split by deep fissures, giving it a striking resemblance to a tortoise or elephant's foot — the source of its common names elephant's foot, turtle back plant and Hottentot bread. From the top of the caudex it sends up a slender, twining vine of heart-shaped leaves each growing season, before retreating back into dormancy.
Description
The defining feature of Dioscorea elephantipes is its caudex, a woody storage organ that sits partly above the soil and slowly enlarges over decades. Its surface breaks into distinct angular plates of thick, corky bark separated by deep grooves, a tessellated pattern that becomes more pronounced with age; large old specimens can reach well over half a metre across, though this takes a very long time to achieve.
From the crown of the caudex the plant produces one or more thin, wiry stems that twine upward through any available support. These bear small, glossy, heart-shaped (cordate) leaves and, in season, modest greenish-yellow flowers — the species is dioecious, so male and female flowers occur on separate plants. The vine is deciduous: it grows, matures and then dies back to the caudex as the plant enters dormancy.
Distribution and habitat
Dioscorea elephantipes is native to South Africa, where it grows in arid to semi-arid scrub across the interior Cape — from the Northern Cape (around Springbok) south to the Clanwilliam and Cederberg area, and eastward through the Eastern Cape as far as Graaff-Reinet, Willowmore and Grahamstown. In cultivation it behaves as a winter grower: it typically leafs out and vines in the cooler months and rests through the hot, dry period, using the water and starch stored in its caudex to survive the long dry season. In habitat the caudex is often partly buried among rocks and low vegetation.
Like other slow-growing caudiciforms drawn from wild habitats, wild-collected plants raise conservation concerns, and mature specimens are occasionally dug from the veld. Although Dioscorea elephantipes itself is not listed under CITES — unlike some other yams, such as the Himalayan Dioscorea deltoidea and the Madagascan Dioscorea populations — nursery-grown, seed-raised plants remain the responsible choice and are what growers should seek out.
Cultivation
The single most important thing to understand about this plant is its seasonal rhythm: water it when it is in leaf and keep it dry when it is dormant. Watering a leafless, resting caudex is the surest way to rot it. Because plants in cultivation can be quirky about exactly when they wake and sleep, the reliable rule is to follow the plant — begin watering when new growth appears and taper off as the vine yellows and dies back, rather than watering by the calendar.
Grow D. elephantipes in a very free-draining, mostly mineral mix in a pot with ample drainage. Give it bright light, with gentle direct sun encouraging sturdier growth; provide a small trellis, stake or frame for the vine to climb. Most growers keep the caudex sitting on top of the soil so its sculptural surface can be admired and so the base stays dry, though young plants are sometimes grown with the caudex buried to speed development. Protect it from frost and from prolonged damp. See Watering and Repotting for general technique.
Propagation
Seed is by far the usual method. Fresh seed sown onto a gritty, well-drained surface and kept lightly moist during the growing season germinates fairly readily, though seedlings are slow and the prized plated caudex takes many years to develop — this is a plant for the patient. Vegetative propagation is not practical in the ordinary way, so seed-raising is both the standard and the most sustainable route. See Propagation — seed for a full walkthrough.
Common problems
- Caudex rot — nearly always the result of watering during dormancy or using a slow-draining mix; the caudex softens and discolours. When in doubt, keep a dormant plant dry.
- Failure to break dormancy — a plant may skip a season or shift its timing; be patient and resist the urge to force it with water before growth resumes.
- Pests — mealybugs can shelter in the fissures of the caudex and at the base of the vine; sap-sucking pests may also trouble the soft new growth. See Pests and diseases.
See also
- Dioscorea — the genus overview
- Soil and potting mix · Watering · Repotting · Propagation — seed · Pests and diseases