Pleiospilos nelii
| Light | Very bright light to full sun; a few hours of direct sun daily keeps the body compact |
|---|---|
| Water | Very sparingly; drench only when actively growing, keep dry through the summer rest |
| Soil | Extremely gritty, mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; USDA zones 9–11, protect from prolonged wet cold |
| Propagation | Seed (primary); occasionally by division of clumps |
| Toxicity | Generally regarded as non-toxic to cats and dogs |
Pleiospilos nelii, commonly called the split rock or cleft stone, is the most popular species of the South African genus Pleiospilos. It forms a fat, near-spherical grey-green body split by a deep central fissure, so that the plant convincingly mimics a weathered pebble until large, satiny flowers erupt from the cleft — usually golden-yellow to orange, or the soft pink of the well-known Royal Flush cultivar.
Description
Pleiospilos nelii is a stemless, clump-capable mesemb made up of one or two pairs of very swollen, wedge-shaped leaves at any one time. Each pair is fused low down and separated above by a pronounced cleft, giving the whole plant the look of a small split stone. The body is grey-green to brownish and finely dotted with darker flecks, a camouflage that lets it disappear among the quartz and stones of its native ground.
New leaf pairs emerge from within the fissure, growing at right angles to the old pair, which shrivels and is absorbed as its water and nutrients are drawn into the new growth. In the wild, flowers appear from the cleft mainly in late winter to spring (they often open in autumn under northern-hemisphere cultivation), opening in the afternoon and closing towards dusk over several days: large for the plant at up to 6–7 cm across, many-petalled and daisy-like, and often faintly coconut-scented. The typical form is orange to golden, while selected lines such as Royal Flush bloom in shades of pink to magenta.
Distribution and habitat
The species is native to the arid interior of South Africa, on the border of the Eastern and Western Cape and extending into the southern Great Karoo, where it grows on stony flats and slopes in the Karoo. There it endures intense sun, long dry spells and sparse, unpredictable rain, rooting in gritty mineral soils among loose rock. Its pebble-like body and dotted colouring are classic examples of the camouflage habit shared across the Aizoaceae, helping it escape the notice of grazing animals. In the wild it is assessed as Near Threatened, having been over-collected for the horticultural trade in the past, with grazing and trampling by livestock now the main pressure on its populations.
Cultivation
Pleiospilos nelii is one of the more forgiving split rocks for a beginner, but it still lives and dies by its watering. Grow it in a small pot of extremely free-draining, mostly mineral mix in the brightest position you can offer; too little light produces a bloated, pale body that splits its skin and topples over.
The single most important rule is to respect its rhythm. Water occasionally in autumn and spring, when it is in active growth, letting the mix dry out completely between drinks. Through the heat of summer the plant rests and should be kept nearly bone dry, and it also takes little water in the depths of winter. The most common way to kill this species is to water while the new leaf pair is still drawing down the old one — doing so bloats the plant and causes it to rot or burst. See Watering and Repotting for general technique.
Propagation
Seed is the usual and most reliable method. The fine seed is sown on the surface of a gritty mix, kept warm and lightly moist until germination, then grown hard and bright to keep seedlings compact. Established multi-headed clumps can also be divided at repotting, teasing rooted heads apart, though the species is slow to offset compared with some other mesembs. See Propagation — seed and Propagation — offsets for details.
Cultivars
The best-known selection is Royal Flush, chosen for its pink to magenta flowers in place of the usual orange. Growers also propagate especially fat, well-marked or heavily clumping forms from seed, but P. nelii is not bred to the elaborate degree seen in some other succulent groups; most named material simply fixes flower colour or body form.
Common problems
- Rot and bursting — nearly always from watering during the summer rest or while the old leaf pair is being reabsorbed; the body swells, splits and collapses.
- Etiolation — too little light gives a swollen, pale, over-tall body that loses its tidy pebble shape.
- Multiple stacked leaf pairs — overfeeding and overwatering can push the plant to keep old pairs instead of shedding them, producing an untidy, congested clump.
- Pests — mealybugs (white fluff, often down in the cleft or at the roots) and the occasional root mealybug are the usual troublemakers; see Pests and diseases.
See also
- Pleiospilos — the genus overview
- Soil and potting mix · Watering · Repotting · Propagation — seed · Propagation — offsets