Dioscorea sylvatica
| Light | Bright, filtered light; a sunny windowsill or lightly shaded greenhouse |
|---|---|
| Water | Water while in leaf; keep dry once the vine dies back for its dormancy |
| Soil | Very free-draining, gritty mineral mix (see Soil and potting mix) |
| Temperature | Keep frost-free; minimum around 8–10 °C, USDA zones 9b–11 |
| Propagation | Seed (primary); rarely by division of the tuber |
| Toxicity | Contains saponins; treat as toxic if eaten by pets or people |
Dioscorea sylvatica is a caudiciform yam from southern Africa, grown by succulent enthusiasts for its cork-barked storage tuber and its annual climbing vine. Compared with its better-known relative Dioscorea elephantipes, it forms a flatter, often lobed and less deeply fissured caudex. Its woodland habitat gives it the common name forest elephant's foot (the epithet sylvatica means "of the woods"). It belongs to the genus Dioscorea in the family Dioscoreaceae.
Description
The most striking feature of Dioscorea sylvatica is its woody caudex — a swollen storage tuber covered in a corky, cracked bark. In this species the caudex tends to be broader, flatter and often more lobed than the tall, dome-shaped tuber of D. elephantipes, with a shallower, less regular pattern of fissures rather than the neat geometric tessellation of its relative. It stays a manageable size in cultivation, making it a rewarding subject for a collection.
Each growing season the caudex sends up one or more slender twining vines bearing heart-shaped (cordate) green leaves. The plant is dioecious, with male and female flowers on separate individuals; the flowers themselves are small and greenish, of more botanical than ornamental interest. As dormancy approaches the vine yellows and dies back, leaving only the caudex until the next flush of growth.
Distribution and habitat
Dioscorea sylvatica is native to southern Africa, where it occurs across parts of South Africa, Eswatini, Mozambique and Zimbabwe. As the epithet sylvatica ("of the woods") suggests, it is often found in and around woodland, bushveld and forest margins, where the vine can scramble up through surrounding shrubs and trees toward the light. In habitat the caudex commonly grows largely buried among leaf litter and rock, with only the upper surface exposed.
Wild populations were heavily reduced during the twentieth century by harvesting for diosgenin — a compound once used as a starting material for cortisone and other steroid hormones — and the species is still collected for traditional medicine and horticulture. It is assessed as Vulnerable on the South African Red List. Nursery-grown, seed-raised plants are the responsible way to add this species to a collection; wild-collected tubers should be avoided.
Cultivation
Dioscorea sylvatica is grown much as other caudiciform Dioscorea. The key is to respect its seasonal rhythm: water regularly while the vine is in active growth, then reduce and withhold water as the foliage yellows and the plant enters dormancy. A completely dormant caudex kept too wet will rot, so it is best kept dry and simply admired through its rest period.
Use a very free-draining, mostly mineral mix and a pot that gives the roots room below the caudex. Growers usually keep the tuber sitting proud of the soil surface so its corky bark can be enjoyed, though young plants are sometimes grown with the caudex buried to speed development, then gradually exposed. Provide bright light and something for the vine to climb — a few stakes or a small trellis — to keep growth tidy. Keep the plant frost-free over winter and see Watering and Repotting for general technique.
Propagation
Seed is the usual and most reliable method. Because the species is dioecious, producing viable seed requires both a male and a female plant flowering together, so many growers simply buy seed or seedlings. Sow onto a warm, gritty surface and keep lightly moist until germination; seedlings form a small tuber early on and are grown on from there. Vegetative increase is difficult — the tuber does not offset freely — though large caudices can occasionally be divided with care. See Propagation — seed for a full walkthrough.
Common problems
- Caudex rot — the commonest cause of loss, almost always from watering during dormancy or using a mix that holds too much moisture; the tuber softens and discolours.
- Failure to break dormancy — a healthy caudex may simply rest longer than expected; keep it dry and warm and be patient rather than forcing water on it.
- Pests — mealybugs can hide in the crevices of the bark and at the base of the vine, and red spider mites may attack the foliage in hot, dry air. See Pests and diseases.
See also
- Dioscorea — the genus overview
- Dioscorea elephantipes — the larger, taller-caudexed relative
- Soil and potting mix · Watering · Repotting · Propagation — seed