Lithops optica
| Light | Very bright light, ideally several hours of direct sun; a sunny south-facing window or bright greenhouse spot |
|---|---|
| Water | Very sparingly, and only during the active growing seasons; keep completely dry while the new bodies absorb the old |
| Soil | Extremely free-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep frost-free and dry in winter; USDA zones 9b–11 |
| Propagation | Seed (primary); division of established clumps |
| Toxicity | Generally regarded as non-toxic to cats and dogs |
Lithops optica is a small, clump-forming "living stone" from the arid coast of Namibia, and one of the most recognisable members of the genus Lithops. Like all living stones it consists of a pair of swollen, fused leaves shaped and coloured to mimic the pebbles among which it grows, with only a slit-like fissure separating the two halves. It is best known in cultivation for the cultivar Lithops optica' 'Rubra, whose bodies are flushed a striking purple-red rather than the grey-green of the wild type, and which produces white, daisy-like flowers in autumn.
Description
Lithops optica forms low clumps of paired leaves, each pair (or "head") a fused, top-shaped body a couple of centimetres across. The flat to slightly domed upper surface is the plant's only window on the world: buried in habitat, it exposes little more than these translucent tops, which allow light down into the tissue below. In the typical form the bodies are grey-green to bluish, while the celebrated 'Rubra' selection is suffused with deep reddish-purple throughout.
Flowers appear in autumn, emerging from the fissure between the two leaves: white, many-petalled and daisy-like, often nearly as wide as the plant itself and opening in the afternoon. Each head flowers only once per season. New leaf pairs form inside the old ones and gradually replace them, the spent outer leaves shrivelling to a papery sheath — the characteristic annual cycle of every Lithops.
Distribution and habitat
The species is native to a small area of the Namib coast in southern Namibia, where it grows in quartzitic and gravelly ground under intense sun and very low rainfall. Much of its moisture comes not from rain but from coastal fog rolling in off the Atlantic. Plants sit almost flush with the surrounding stones, an extreme example of the camouflage ("mimicry") that protects living stones from grazing animals.
Cultivation
Lithops optica is grown much as other living stones, and its needs are simple but strict — overwatering, especially at the wrong time of year, is the usual cause of death. Grow it in a very free-draining, almost entirely mineral mix in a pot deep enough for its long taproot, and give it the brightest light you can: in too little light the bodies stretch, pale and lose their compact, stone-like form. The red pigment of 'Rubra' also develops best under strong light.
Watering must follow the plant's annual rhythm rather than the calendar on the wall. Water lightly during the active growth periods in spring and autumn, allowing the mix to dry completely between drinks. Crucially, keep the plant bone dry through winter and through its summer rest, and stop watering altogether while the new leaf pair is drawing down the old one — watering during this exchange causes the plant to bloat, split or rot. See Watering and Repotting for general technique.
Propagation
Seed is the standard and most rewarding method. Sown on a fine mineral surface and kept warm and lightly humid, the tiny seeds germinate readily, though seedlings are slow and are grown on for a year or more before they take on adult form and colour. See Propagation — seed for a full walkthrough.
Established clumps can also be divided, ideally at the start of a growing season, taking care to keep as much of each head's root as possible. Because 'Rubra' comes largely true from seed of selected parents, most plants in the trade are seed-raised rather than divided.
Cultivars
By far the best known selection is Lithops optica' 'Rubra', prized for its purple-red bodies and long popular with collectors as an easy splash of colour among otherwise stony-coloured living stones. Its care is identical to that of the species; it simply rewards strong light with deeper colour.
Common problems
- Rot — almost always from watering during winter, summer dormancy, or the leaf-exchange period, or from a mix that holds too much moisture; the body goes soft and mushy.
- Etiolation — too little light makes the body elongate upward and turn pale, losing the flat, pebble-like profile; 'Rubra' also loses its red flush.
- Stacking / failure to shed — over-watering can leave the plant carrying several generations of old leaves at once instead of cleanly renewing a single pair.
- Pests — mealybugs (white fluff, often down in the fissure or at the roots) and spider mites are the usual offenders; see Pests and diseases.
See also
- Lithops — the genus overview
- Soil and potting mix · Watering · Repotting · Propagation — seed · Pests and diseases