Monadenium rhizophorum
| Light | Bright light to light shade; protect from harsh midday sun |
|---|---|
| Water | Moderately in growth; keep dry and rested through the cool season |
| Soil | Very free-draining gritty mix (see Soil and potting mix) |
| Temperature | Warmth-loving; keep above 10 °C, no frost |
| Propagation | Rhizome division, offsets, stem cuttings, or seed |
| Toxicity | Caustic milky sap — toxic and irritant; keep away from pets and children |
Monadenium rhizophorum is a small, clumping caudiciform succulent in the family Euphorbiaceae, native to East Africa and closely allied to the genus Euphorbia. It spreads underground by fleshy rhizomes, sending up short, knobby green stems that give a mature plant the look of a low, creeping colony rather than a single upright specimen. Like all members of Monadenium it carries a milky, irritant sap and produces the curious hooded flower structures (cyathia) that distinguish the group.
Description
Monadenium rhizophorum grows from a swollen, partly subterranean rootstock that creeps horizontally as a rhizome, budding new growth points as it travels. The above-ground stems are short and cylindrical, their surfaces broken into rows of low, rounded tubercles that give the plant its characteristic knobby texture. Small, thin leaves appear near the stem tips during active growth and are shed as conditions dry, leaving the succulent green stems to carry on the work of photosynthesis.
As with other members of the genus, the flowers are not typical blooms but cyathia — compact false-flowers wrapped in a fused, hood-like bract. They are modest and easy to overlook, but reward a close look. The rhizomatous habit means a happy plant slowly widens into a small colony over several seasons.
Distribution and habitat
The species is native to East Africa, where plants of this group typically grow in seasonally dry bushland and rocky ground, rooting into gritty, well-drained soils among grasses and low scrub. Growth is tied to the seasons: plants swell and leaf out with the rains, then retreat to their fleshy roots and rhizomes through the long dry period. This wet-and-dry rhythm is the key to understanding the plant in cultivation.
Cultivation
Monadenium rhizophorum is an easygoing, warmth-loving succulent for anyone who already grows Euphorbia or other caudiciforms. Pot it in a very free-draining, mostly mineral mix — the rhizome and rootstock rot quickly in soggy conditions. Because the plant spreads sideways, a wider, shallower pot suits it better than a deep one and gives the rhizomes room to run.
Give it bright light for compact, well-coloured growth, with a little shade from the fiercest midday sun. Water moderately while the plant is in active growth and leaf, letting the mix approach dryness between soakings; then reduce watering sharply as growth slows and keep it nearly dry through the cool, resting season. Keep it warm — this is not a frost-hardy plant, and prolonged cold combined with damp is the surest way to lose it. See Watering and Repotting for general technique.
A word of caution: like all euphorbias, it bleeds a milky white latex when cut or bruised. The sap is caustic and can badly irritate skin and eyes, so wear gloves, wash any contact off promptly, and keep the plant out of reach of pets and children.
Propagation
The rhizomatous habit makes M. rhizophorum unusually easy to increase. The simplest method is division: lift a clump during repotting and separate a section of rhizome that carries its own growth point and roots, then pot it up in the same gritty mix. Detached offsets and stem cuttings also root readily once the cut end has been allowed to dry and callus for a few days — an essential step with any euphorbia to seal the sap and prevent rot. Seed is possible where it can be obtained. See Propagation — offsets and Propagation — cuttings for step-by-step guidance.
Common problems
- Rot — the commonest cause of loss; almost always from a wet, slow-draining mix or watering during the cool rest. The rhizome or stem base softens and discolours.
- Etiolation — too little light draws the stems out pale and weak, blurring the tidy knobby form.
- Pests — mealybugs (white fluff between the tubercles and around the roots) and the occasional spider mite are the usual offenders. See Pests and diseases.
- Sap irritation — not a plant problem but a grower one: the caustic latex demands care whenever you cut, divide or repot.
See also
- Monadenium — the genus overview
- Euphorbia — the closely related (and now often merged) genus
- Grafting · Soil and potting mix · Watering · Propagation — cuttings · Propagation — offsets · Repotting · Pests and diseases