Orbea dummeri
| Light | Bright light to light shade; protect from harsh midday sun |
|---|---|
| Water | Regularly in the warm growing season, letting the mix dry between waterings; keep nearly dry in winter |
| Soil | Very free-draining, gritty mineral mix (see Soil and potting mix) |
| Temperature | Warmth-loving; keep above about 10 °C, frost-tender |
| Propagation | Stem cuttings (easy); seed |
| Toxicity | Generally regarded as non-toxic; unlike many relatives in the family, stapeliads lack milky latex and have clear, watery sap, but as with any plant it is best kept away from pets that may chew it |
Orbea dummeri is an East African stapeliad — a clump-forming, leafless succulent in the milkweed family Apocynaceae — grown for its robust, sharply toothed green stems and its star-shaped, hairy flowers in shades of greenish-yellow to olive-green. Like other members of the genus Orbea, it spreads into low mats and produces its curious blooms low on the clump. It was long known under the name Caralluma dummeri, and is still often sold that way.
Description
Orbea dummeri forms spreading clumps of erect to sprawling (sometimes decumbent) stems, up to around 10 centimetres tall and squarish in cross-section, with four angles lined by prominent, spreading teeth. The stems are soft-fleshed, grey-green to bright green, and often take on reddish or purplish striations and mottling in strong light. As with all stapeliads there are no true leaves — the green stems do the work of photosynthesis, and any leaf is reduced to a tiny, quickly-shed point at the tip of each tooth.
The flowers are the main draw: moderate-sized, roughly 2.5–4 centimetres across, star-shaped, with five spreading, triangular lobes. The colour is greenish-yellow to olive-green, sometimes nearly chartreuse, and the corolla surface is distinctly hairy, the lobes edged and tipped with short, pale bristly hairs. A raised ring (the annulus), characteristic of the genus, sits at the centre around the compact crown of the flower. Unlike the strongly carrion-scented blooms of many stapeliads, those of O. dummeri give off only a faint, slightly sour odour, and they are pollinated by small flies and other insects.
Distribution and habitat
The species occurs in East Africa — in Uganda, Kenya, Tanzania and Burundi, extending into the eastern Democratic Republic of the Congo. It grows in seasonally dry bush and grassland, often tucked into the shade of shrubs, rocks or grass tussocks where the roots stay cool and the clump is sheltered from the fiercest sun. Plants experience a warm wet season followed by a long dry rest, a rhythm worth remembering when watering in cultivation.
Cultivation
Orbea dummeri is an undemanding stapeliad for a warm, bright spot and is a good choice for growers new to the group. Plant it in a wide, shallow container of very free-draining, mostly mineral mix, as the clump spreads outward rather than down. Give it bright light with a little shade from the most intense midday sun; too much shade makes the stems thin and weak, while some sun brings out the reddish stem colour and encourages flowering.
Water regularly through the warm months once the mix has dried, then reduce sharply as temperatures fall and keep the plant nearly dry over winter. Cold, damp conditions are the main danger — the fleshy stems rot quickly if left wet and cool. Keep it above roughly 10 °C and never expose it to frost. See Watering and Repotting for general technique.
Propagation
Propagation is easy from stem cuttings. Detach a healthy stem or a small cluster, let the cut end callus for a few days, then set it on a gritty, barely-moist mix; rooting is usually quick in warm weather, and clumps can also be lifted and divided when repotting. The plant can be raised from seed as well, though seed is less commonly available; sow on a warm mineral surface as described in Propagation — seed.
Common problems
- Rot — the commonest cause of loss, almost always from overwatering, a slow-draining mix, or cold wet conditions; stems soften, blacken and collapse from the base.
- Mealybugs — hide in the crevices between stems and on the roots; watch for white fluff and treat promptly (see Pests and diseases).
- Etiolation — in too little light the stems grow thin, pale and floppy and the plant flowers poorly.
- Sooty mould and ants — often follow a sap-sucking infestation and signal a pest problem to track down.
See also
- Orbea — the genus overview
- Soil and potting mix · Watering · Repotting · Propagation — cuttings · Pests and diseases