Othonna euphorbioides
| Light | Bright light to full sun; a sunny windowsill or lightly shaded greenhouse |
|---|---|
| Water | Winter grower — water in the cool months, keep dry through summer dormancy |
| Soil | Very free-draining, gritty mineral mix (see Soil and potting mix) |
| Temperature | Keep frost-free in cultivation; USDA zones 9b–11 |
| Propagation | Seed (primary); cuttings possible but slow |
| Toxicity | No toxicity documented; treat as unknown and keep away from curious pets |
Othonna euphorbioides is a spiny, caudiciform member of the daisy family (Asteraceae), endemic to Namaqualand in the arid northwest of South Africa and prized by collectors of winter-growing succulents. It forms a knobby, swollen stem or caudex armoured with persistent hardened flower stalks, giving it a fierce, gnarled look. It is one of the more distinctive shrubby species in the genus Othonna.
Description
Othonna euphorbioides builds up a thick, tuberous, knobbly stem that becomes swollen and woody with age — up to about 300 mm thick and clothed in a tough, peeling, yellowish-grey bark — often branching into a low, congested shrublet. The surface is roughened by the raised scars and bases of old growth, and — most characteristically — by the dried, spine-like remains of previous flower stalks, which harden and persist to form a defensive armour reminiscent of a spiny Euphorbia (hence the epithet euphorbioides).
Small, fleshy leaves cluster at the growing tips, appearing mainly during the active winter season and often shed as the plant goes dormant in summer. The flower heads are small — only about 5 mm across — and yellow to greenish-yellow, borne in clusters on short, stiff stalks and sweetly scented; they appear in the cool winter months. Once the heads fall, these stalks stiffen and persist, becoming the spines that armour the stem.
Distribution and habitat
The species is endemic to South Africa, restricted to Namaqualand in the Northern Cape, from the Richtersveld and Bushmanland south to the Kamiesberg. It grows in cracks and fissures on exposed granite domes and rock sheets, at roughly 1000–1600 m, in a winter-rainfall climate — enduring hot, dry summers and receiving most of its moisture, along with occasional light frost, during the cool winter growing months. This habitat rhythm is the key to understanding its cultivation.
Cultivation
Othonna euphorbioides is a rewarding but particular plant, and the single most important thing to get right is its growth cycle: it is a winter grower. Water it during the cool, low-light months when it is in active growth, and keep it dry — or nearly so — through the heat of summer, when it rests. Watering a dormant caudiciform in hot weather is the fastest route to rot.
Grow it in a very free-draining, mostly mineral mix in a pot that suits the size of the caudex, and give it bright light with some direct sun to keep the body compact and the spines well formed. Though it endures light frost in habitat, it is safest kept frost-free in cultivation. As with most caudiciforms, err on the side of underwatering; the swollen stem stores considerable reserves. See Watering and Repotting for general technique, and note that many growers raise the caudex slightly at each repotting to show off its knobby form.
Propagation
Seed is the standard and most reliable method. Sow in autumn onto a gritty, mineral surface, cover lightly with fine grit or pumice, and keep lightly moist until germination, which is usually quick; then grow the seedlings on hard and bright. Cuttings can sometimes be rooted but are slower and less dependable, and they do not readily reproduce the fat caudex — seedlings develop a far better swollen base over time. See Propagation — seed and Propagation — cuttings for full walkthroughs.
Common problems
- Rot — almost always from watering during summer dormancy or from a slow-draining mix; the caudex softens and discolours.
- Loss of form — too little light or overly rich, moist conditions produce weak, drawn growth and a poorly defined caudex.
- Pests — mealybugs (white fluff in the leaf clusters and stem crevices) and root mealybugs are the usual culprits; see Pests and diseases.
See also
- Othonna — the genus overview
- Soil and potting mix · Watering · Repotting · Propagation — seed · Propagation — cuttings