Titanopsis
Titanopsis is a small South African genus of clump-forming mesembs in the ice plant family (Aizoaceae), instantly recognised by the wart-like tubercles crusting the tips of their thick, spoon-shaped leaves. This rough, mineral-encrusted surface is superb camouflage: at rest the plants blend almost perfectly into the weathered limestone rubble they grow among, which has earned them common names such as concrete leaf, limestone plant and jewel weed.
Description
Plants in Titanopsis form low, tight rosettes of fleshy leaves that spread slowly into small clumps. Each leaf is club- or spoon-shaped — narrow at the base and widening to a flattened, angled tip — and it is this truncated tip that carries the genus's signature feature: a dense encrustation of raised, wart-like tubercles. Depending on the species these bumps range from blue-green and grey to rusty and bronze, giving the flattened leaf ends the look and texture of chipped stone.
The rosettes are small, typically only a few centimetres across, and hug the ground closely. Flowers appear from the centre of the rosette in autumn and winter, opening in the afternoon sun. They are daisy-like (though, as in all mesembs, not true daisies) and are usually yellow to orange, sometimes with paler outer petals, and generously sized relative to the compact plant.
Distribution
Titanopsis is native to the arid interior of southern Africa, with a scattered, disjunct distribution across the Karoo and neighbouring dry interior of South Africa and into southern Namibia. The plants are limestone specialists, growing wedged among calcareous gravel and weathered limestone rock in exposed, low-rainfall country. Their tuberculate leaf tips echo the surrounding stone so closely that the rosettes can be almost impossible to spot when not in flower — a form of protective mimicry shared with several other Karoo mesembs.
Notable species
- Titanopsis calcarea — the best-known species; grey-green leaves tipped with rusty, limestone-like warts and cheerful yellow-orange flowers.
- Titanopsis schwantesii — softer bluish leaves with more rounded tubercles.
- Titanopsis hugo-schlechteri — a compact, heavily encrusted species with a particularly stony appearance.
- Titanopsis primosii — a smaller-growing species, often treated as a form of T. schwantesii.
Cultivation
Like most Karoo mesembs, Titanopsis is undemanding once its seasonal rhythm is understood, but it will not tolerate being kept wet. Grow it in a very gritty, sharply draining, mostly mineral mix with plenty of grit or crushed limestone, in the brightest position you can offer — strong light keeps the rosettes tight and the tubercles well coloured, while too little light causes the leaves to stretch and lose their compact, stony character.
Growth season varies with a species' origin, and it pays to know which plant you have: the popular eastern species such as T. calcarea come from summer-rainfall country and take some water through the warmer months, whereas the western species such as T. schwantesii and T. hugo-schlechteri are winter growers that flower with the winter rains. Whatever the rhythm, water only while the plant is in active growth, always let the mix dry fully between drinks, and keep it dry through its rest — whether that rest falls in summer or in winter. Protect from frost and from prolonged wet, and give good airflow. See Watering and Repotting for general technique, and note that Titanopsis is comparatively forgiving, making it a good introduction to the mesembs for growers moving on from Lithops and Faucaria.
Propagation
The genus is readily raised from seed, which is the usual way to increase a collection. Sow the fine seed on the surface of a mineral mix in the cooler months, keep it lightly humid until germination, then grow the seedlings hard in bright light. Established clumps can also be divided, and individual heads with roots can re-establish. See Propagation — seed and Propagation — offsets for details.
Common problems
- Rot — by far the commonest cause of loss, from overwatering, a soil that holds moisture, or water sitting on the rosette during a dry rest.
- Etiolation — insufficient light makes the leaves elongate and soft, so the rosettes open out and lose their tight, stone-like look.
- Pests — mealybugs can hide down among the leaf bases and in the root zone; watch also for the usual sap-suckers under glass. See Pests and diseases.
See also
- Aizoaceae — the ice plant family
- Lithops · Faucaria · Pleiospilos — related Karoo mesembs
- Soil and potting mix · Watering · Propagation — seed · Repotting