Orbea semota
| Light | Bright light with some shade from harsh midday sun; too little light spoils flower colour and stem form |
|---|---|
| Water | Moderate in the growing season, letting the mix dry between waterings; keep dry and cool in winter |
| Soil | Open, gritty, fast-draining mix (see Soil and potting mix) |
| Temperature | Warmth in summer; keep above about 8–10 °C in winter and avoid frost |
| Propagation | Stem cuttings (easy) and seed |
| Toxicity | Like most milkweeds, best kept away from pets and children as a precaution; not a notable poisoning risk |
Orbea semota is an East African stapeliad — a clump-forming, leafless succulent in the milkweed family Apocynaceae — grown for its tidy, erect green stems and its striking star-shaped flowers, which range from dark red-brown and maroon to (in some forms) clear yellow. Like most stapeliads, the blooms are fly-pollinated and give off a carrion- or dung-like smell. It is one of the easier, more beginner-friendly members of the genus Orbea.
Description
Orbea semota forms low, spreading clumps of upright four-angled stems, typically a few centimetres to around 10 cm tall. The stems are soft and green, often flushed with purple or grey in strong light, with rows of firm teeth along the angles that give the plant a neat, geometric look. Unlike leafy succulents, the stems themselves do the work of photosynthesis; true leaves are reduced to tiny, short-lived points on the teeth.
The flowers are the main attraction. Borne singly or a few together near the base of the stems, they are flat, five-lobed stars, commonly 3–5 cm across, in tones of dark red-brown, chocolate and maroon — or, in the form known as var. lutea, clear yellow — sometimes finely wrinkled or barred and edged with fine, vibratile hairs. At the centre sits the raised, ringed corona typical of the stapeliads. Like other members of the group, the flowers give off a foul, carrion- or dung-like odour that draws the flies that pollinate them.
Distribution and habitat
The species grows in East Africa, in the drier bush and rocky grassland country of the region (including parts of Rwanda, Kenya and Tanzania). Plants typically shelter among rocks, grasses and low shrubs, rooting in gritty, sharply drained ground and enjoying light overhead shade during the fiercest part of the day. This habitat — seasonal rain followed by long dry spells and warmth — is the key to understanding how to grow it well.
Cultivation
Orbea semota is one of the easier stapeliads and a good introduction to the group. Grow it in a wide, shallow pot in an open, very free-draining mineral mix, as the fleshy stems rot quickly in soggy or airless compost. Give it bright light with some protection from scorching midday sun; good light keeps the stems compact and brings out the purple flush and the best flower colour, while deep shade produces weak, pale, floppy growth.
Water moderately through the warm growing season, always letting the mix dry out before watering again, then keep the plant dry and cool over winter to prevent rot and encourage flowering. Warmth and fresh air suit it; protect it from frost. See Watering and Repotting for general technique, and lift and refresh crowded clumps every year or two.
Propagation
Propagation is easy and one of the pleasures of growing stapeliads. Detach a healthy stem, let the cut end dry and callus for a few days, then set it on or just into a gritty mix; it roots readily in warm conditions. Because clumps offset freely, division at repotting time is another simple route. The species also sets seed in the characteristic paired, horn-like follicles, whose plumed seeds germinate well when fresh. See Propagation — cuttings, Propagation — offsets and Propagation — seed for full walkthroughs.
Common problems
- Rot — by far the commonest cause of loss, from overwatering, a slow-draining mix, or cold damp winters; stems turn soft, translucent and blacken. Take cuttings from any firm growth to save a collapsing plant.
- Etiolation — too little light gives thin, stretched, pale stems and poor flowering.
- Pests — mealybugs (white fluff at the stem bases and roots) and, under glass, spider mites are the usual offenders; watch the root zone as well as the stems. See Pests and diseases.
See also
- Orbea — the genus overview
- Stapeliad · Soil and potting mix · Watering · Repotting
- Propagation — cuttings · Propagation — offsets · Propagation — seed