Othonna retrorsa
| Light | Bright light to full sun; strong light keeps growth compact |
|---|---|
| Water | Water during the cool growing season (roughly autumn to spring); keep dry when dormant in the heat of summer |
| Soil | Very gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Frost-tender in cultivation; protect from freezing, though it endures cold nights at altitude in habitat |
| Propagation | Seed (best); the multi-headed caudex can also be divided |
| Toxicity | No toxicity specifically reported; as a relative of Senecio, treat with caution and keep away from pets |
Othonna retrorsa is a small, cushion-forming caudiciform member of the daisy family (Asteraceae), endemic to the arid, winter-rainfall Namaqualand region of the Northern Cape, South Africa. It forms a low, many-headed woolly caudex clothed with the persistent, reflexed (retrorse) bases of shed leaves — the feature that gives the species its name — and bears rosettes of distinctive, leathery, prominently net-veined leaves. It is sought after by succulent collectors, and illegal collection of wild plants is now its principal conservation threat.
Description
Othonna retrorsa forms a small, suberect caudex (only a few centimetres thick and up to roughly 8 cm high), simple or divided into several woolly heads, so that older plants build a low cushion reaching about 10 cm tall and up to 30 cm across. Its most characteristic feature is the way old leaf bases are retained along the caudex, curving sharply downward (retrorse) to leave a textured, woolly, tiered column that persists long after the blades themselves have withered.
The leaves are carried in dense rosettes at the tips of the caudex heads, typically appearing during the cool growing season and dropping as the plant moves into dormancy. Rather than being simply fleshy, they are rigid and leathery, chalky grey-green, and prominently netted-veined on both surfaces, with hardened (cartilaginous) margins bearing small white teeth — a highly distinctive foliage for the genus. As with other members of the genus, the flowers are small daisy-like capitula, yellow, carried on slender scapes well above the foliage. Like most caudiciform Othonna, it is a slow-growing, long-lived plant that rewards patience.
Distribution and habitat
The species is a South African endemic, restricted to the semi-arid, winter-rainfall Namaqualand region of the Northern Cape — broadly from around Springbok to Kliprand and west toward Kotzesrus — within the Succulent Karoo. It grows on exposed granite, tucked into cracks in boulders and shallow, gritty sandy depressions on rocky slopes, generally at higher altitude, and is adapted to a long, hot, essentially rainless summer during which it rests.
Understanding this winter-growing, summer-dormant rhythm is the single most important key to keeping the plant well.
Cultivation
Othonna retrorsa is grown much like other winter-growing caudiciform succulents. It is a "winter grower": it wakes and puts on leaves as temperatures cool and days shorten, then drops its foliage and rests through the heat of summer. Match your Watering to this cycle — water when the plant is in active leaf and the mix has dried, and keep it dry or nearly so during summer dormancy to avoid rotting the caudex.
Grow it in a very gritty, mostly mineral mix in a pot with excellent drainage, and give it bright light to full sun; strong light keeps the plant compact and encourages the tight, characterful growth collectors seek. Protect the plant from frost. Many growers raise the caudex slightly at repotting time to display the woolly stem and its downward-curving leaf bases.
Propagation
Seed is the most reliable method and gives the best caudex development; sow onto a warm, gritty surface and keep lightly moist until seedlings establish (see Propagation — seed). Because the plant is many-headed, an established caudex can also be divided, though the pieces re-establish slowly; simple stem cuttings are rarely used with caudiciform Othonna and will not readily rebuild the swollen stem, so seed is generally preferred for a natural-looking plant. See also Propagation — cuttings.
Conservation
Othonna retrorsa is assessed as Endangered on the Red List of South African Plants. It is a slow-growing, range-restricted endemic, and its populations are declining chiefly because of illegal collection for the specialist succulent trade, with overgrazing a lesser, local pressure. Collectors should obtain seed-grown or otherwise legitimately propagated stock rather than wild-collected plants; wild collection and export of South African succulents are subject to permit requirements and legal restriction.
Common problems
- Rot — the commonest cause of loss, almost always from watering during summer dormancy or from a slow-draining mix; the caudex softens and discolours.
- Loss of form — too little light causes weak, stretched (etiolated) growth and a soft, elongated habit instead of a compact caudex.
- Pests — watch for mealybugs sheltering among the persistent leaf bases and around the roots; see Pests and diseases.
See also
- Othonna — the genus overview
- Soil and potting mix · Watering · Repotting · Propagation — seed · Propagation — cuttings