Euphorbia groenewaldii
| Light | Bright light to full sun; some shade in the hottest part of the day |
|---|---|
| Water | Sparingly in growth; keep dry through winter, protecting the tuber from rot |
| Soil | Very free-draining, gritty mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; likes warmth, USDA zones 9b–11 |
| Propagation | Seed; cuttings of the branches |
| Toxicity | Toxic; the milky latex irritates skin and eyes (see Euphorbia) |
Euphorbia groenewaldii is a rare, dwarf, caudiciform succulent from a very small area of the Limpopo province in South Africa. It grows from a large, partly buried tuberous rootstock that gives rise to short, spreading branches lined with prominent tubercles and paired spines, so that most of the plant's bulk sits hidden below the soil. It is one of the most sought-after and strictly protected members of the genus Euphorbia.
Description
Euphorbia groenewaldii is a geophytic, caudiciform succulent built around a thick, woody, tuberous root that can be considerably larger than the visible parts of the plant. From the crown of this tuber arise several short branches, typically only a few centimetres long, which are spirally twisted and set with rows of prominent tubercles. Pairs of small, hardened spines run along the branches, giving them a rough, armoured look.
The plant is monoecious: male and female flowers occur on the same plant, so a single specimen can set seed. The small cyathia — the specialised Euphorbia flower-like structures — are borne in clusters near the branch tips, with the central cyathium of each group bearing only male flowers and the outer two bearing both sexes, and carry yellow nectar glands. Like all euphorbias, every part exudes a milky white latex when cut or broken.
Distribution and habitat
The species is a narrow endemic, known only from a restricted area near Polokwane in the Limpopo province of South Africa. It grows on rocky outcrops and stony granite hills in well-drained ground, where the bulk of the plant is drawn down among stones and grasses and only the branch tips show at the surface — an arrangement that shelters it from grazing, fire, sun and drought alike.
Its tiny natural range and the pressure of illegal collecting make it highly vulnerable, and it is assessed as Critically Endangered, with an extent of occurrence of only a few square kilometres and much of the wild population already lost. Like the whole genus, it is listed under CITES Appendix II, and collecting plants from habitat is illegal. Nursery-raised, legally propagated specimens are the only ones that should be bought or traded.
Cultivation
Grow Euphorbia groenewaldii much as you would other tuberous, winter-dormant euphorbias. It needs a very free-draining, mostly mineral mix and a deep pot to accommodate the tuber. Give it bright light to full sun; too little light causes weak, drawn growth, while some midday shade in the fiercest heat prevents scorching.
Water sparingly while the plant is in active growth and let the mix dry out completely between waterings. The buried tuber is the plant's weak point: excess moisture, especially in the cool season, leads quickly to rot. Keep it dry and frost-free through winter. Some growers raise the tuber a little at repotting time to show it off, but a partly buried caudex is generally more forgiving. Handle the plant with care — the latex is a skin and eye irritant, so wear gloves and wash any sap off promptly.
Propagation
Seed is a satisfying method, and because the species is monoecious a single plant can produce viable seed; sow the fresh seed on a warm, gritty surface (see Propagation — seed). Branch cuttings can also be rooted: let the cut end dry and callus for several days to stop the flow of latex before setting it in a dry, gritty mix. Cutting-grown plants may not develop as fine a tuber as seed-raised ones.
Common problems
- Rot — the commonest cause of loss; almost always from overwatering or a mix that holds moisture around the tuber.
- Etiolation — too little light produces pale, elongated, weak branches instead of the compact natural form.
- Pests — mealybugs (white fluff between the tubercles and at the roots) and spider mites are the usual offenders; see Pests and diseases.
Legal status
Euphorbia groenewaldii is a protected species in South Africa and, as a member of the family, is listed under CITES Appendix II, which regulates international trade in wild-collected plants. Because of its rarity it is a frequent target of illegal collection. Only legally propagated, documented nursery plants should be acquired; wild collection is prohibited and damaging to the few remaining populations.
See also
- Euphorbia — the genus overview
- Grafting · Soil and potting mix · Watering · Propagation — seed · Propagation — cuttings · Pests and diseases