Conophytum calculus
| Light | Bright light with protection from harsh midday sun; good ventilation |
|---|---|
| Water | Only during the autumn–winter growth season; keep bone-dry through summer dormancy |
| Soil | Very gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Frost-free; USDA zones 9b–11, cool and dry in winter |
| Propagation | Seed; division of older clumps |
| Toxicity | Not known to be toxic to cats or dogs |
Conophytum calculus is a small, dwarf succulent in the ice-plant family Aizoaceae, famous for looking almost exactly like a smooth, rounded pebble. Each plant body is a firm, near-spherical grey-green cono with a barely visible fissure on top, and in autumn it produces yellow flowers that open at night and are strongly scented. It belongs to the genus Conophytum, a group of mimicry mesembs beloved by collectors of small windowsill succulents.
Description
Conophytum calculus consists of one or more paired-leaf bodies fused into a smooth, obconic-to-spherical unit, typically a few centimetres across. The surface is chalky grey-green to bluish, matte and unmarked, with only a small slit-like mouth on the upper face — an adaptation that helps the plant blend in among the quartz pebbles of its habitat. With age a single head divides to form a tight, low mound of many rounded bodies.
Flowering comes in autumn. The blooms are yellow, opening at night from the top fissure and releasing a strong sweet fragrance, which points to moth pollination in the wild. Like other conos, each body lives for a season: the old outer skin dries to a papery sheath and a fresh body emerges from within during the next growth cycle.
Distribution and habitat
The species is native to the arid western regions of South Africa, where it grows in the winter-rainfall zone. Plants are typically found nestled among pale quartz gravel on exposed rocky flats and slopes, where their pebble-like form makes them extremely difficult to spot when not in flower. The climate is defined by hot, dry summers and cooler, moister winters — the rhythm that governs the plant's growth cycle.
Habitat populations can be localised and vulnerable to illegal collection; as with all Conophytum, growers should seek nursery- or seed-raised plants rather than wild-collected specimens.
Cultivation
The single most important thing to get right with Conophytum calculus is the watering rhythm, which must follow its winter-growing habit. Water during the cooler autumn and winter growth period, letting the mix dry between soakings, and keep the plant essentially dry through the heat of summer while it rests inside its papery sheath. Overwatering — especially in summer dormancy — is the usual cause of rot and loss.
Grow it in a shallow pot in a very gritty, mostly mineral mix, in bright light with a little shade from the fiercest midday sun and plenty of fresh air. A cool, dry winter and good ventilation keep the bodies firm and encourage flowering. See Watering and Repotting for general technique, and be gentle when handling the fragile new bodies.
Propagation
Seed is the most reliable route and produces large numbers of tiny seedlings that are grown on slowly over several seasons; sow onto a fine mineral surface and keep humid and warm to germinate. See Propagation — seed for a full walkthrough.
Older clumps can also be divided: lift a mound, separate rooted or near-rooted heads, allow the cut surfaces to callus briefly, then pot up at the start of the growth season. See Propagation — offsets for the general approach to dividing clustering plants.
Common problems
- Rot — almost always from watering during summer dormancy or from a mix that holds too much moisture; bodies go soft and translucent.
- Failure to flower — usually too little light or a growth season that was kept too warm and wet; a cool, bright, airy autumn helps.
- Pests — mealybugs can hide between the bodies and in the old sheaths, and root mealybugs may lurk in the soil. See Pests and diseases.
See also
- Conophytum — the genus overview
- Soil and potting mix · Watering · Propagation — seed · Propagation — offsets · Repotting · Pests and diseases