Caralluma
Caralluma is a genus of clump-forming, angular-stemmed stapeliad succulents in the milkweed family Apocynaceae, native to the dry country of Africa, the Arabian Peninsula and the Indian subcontinent. Once a large and loosely defined group, Caralluma has been substantially trimmed by modern study, with many familiar plants moved into segregate genera such as Monolluma, Caudanthera, Apteranthes, Desmidorchis and others — so a plant sold under an old Caralluma name may now sit elsewhere botanically.
Like their better-known relatives the stapelias and huernias, carallumas are leafless stem succulents whose small, intricate, often carrion-scented flowers are pollinated by flies. They are prized by stapeliad enthusiasts for their sculptural, upright stems and their curious star-shaped blooms.
Description
Caralluma plants are small to medium leafless succulents that grow from a shallow, fibrous root system into clumps of erect or spreading stems. The stems are typically four-angled (square in cross-section) and toothed along the ridges, ranging from a fresh grey-green to purplish, often mottled or flushed with red in strong sun. What look like spines are soft, tooth-like tubercles rather than the true spines of a cactus — carallumas are not cacti but succulent members of the Apocynaceae, a case of convergent evolution with the New World cactus family.
Flowers appear singly or in small clusters, usually toward the stem tips, and follow the classic stapeliad pattern: five-lobed, star- or bell-shaped, and frequently dark maroon, purple or intricately patterned. Many are pollinated by flies and give off a faint to distinctly unpleasant scent to attract them. As with all members of the family, cut or broken stems exude a clear to milky sap.
Distribution and habitat
The genus, in both its broad historical sense and its narrower modern one, is centred on the arid and semi-arid Old World — North and East Africa, the Arabian Peninsula, and dry parts of the Indian subcontinent. Plants grow in stony, well-drained ground: rocky slopes, gravel flats and the shade of low shrubs, where they endure long dry seasons and considerable heat. Several species have a long local history of use as famine or thirst-quenching foods in their home ranges.
Taxonomy
Caralluma has a tangled history. As traditionally circumscribed it held well over a hundred species, but molecular and morphological work has shown the old genus to be a mixture of distinct lineages. Many species have accordingly been reassigned to segregate genera, including:
- Monolluma — e.g. the plant long grown as Caralluma socotrana
- Caudanthera — a few stout species of Arabia, NE Africa and the Indian region, such as the former Caralluma edulis
- Desmidorchis — robust African and Arabian species such as the former Caralluma penicillata and Caralluma acutangula
- Apteranthes — Mediterranean and North African species such as the former Caralluma europaea
Because of this, catalogue and label names lag well behind current botany. When identifying a plant it is worth checking whether its name is still placed in Caralluma or has been transferred elsewhere.
Notable species
- Caralluma adscendens — a variable Indian species with several recognised varieties
- Caralluma fimbriata — a small Indian species long eaten as a famine food, thirst-quencher and folk appetite-suppressant
- Caralluma arachnoidea — an East African species (Ethiopia to Tanzania) whose flowers are fringed with fine cobweb-like hairs
- Caralluma priogonium — an East African species with prominently toothed stem angles
Several plants once central to the genus have since been transferred out of it: the old Caralluma europaea now sits in Apteranthes, Caralluma socotrana in Monolluma, and Caralluma penicillata and Caralluma acutangula in Desmidorchis — so these are best sought under their newer names.
Cultivation
Carallumas are grown much like other stapeliads and reward the same routine as Stapelia and Huernia. They need warmth, bright light and, above all, sharp drainage. Plant them in a gritty, mostly mineral mix in a shallow, wide pot that suits their spreading habit, and give the brightest position you can — good light keeps the stems compact and brings out their reddish tints, while too little causes weak, etiolated growth.
Water moderately through the warm growing season, always letting the mix dry between drinks, and keep the plants dry and warm through winter, when the shallow roots are especially prone to rot. Most species resent cold, wet conditions and are best kept frost-free. See Watering and Repotting for general technique.
Common problems
- Basal and stem rot — the main cause of loss, usually from a cold, wet, or poorly drained root run; affected stems soften, blacken and collapse.
- Mealybugs — hide in stem crevices and among the roots; a frequent pest of stapeliads (see Pests and diseases).
- Etiolation — thin, over-tall, pale stems from insufficient light.
Propagation
Stem cuttings are the easiest and most reliable method: detach a healthy stem segment, let the cut end callus for several days, then set it in a dry, gritty mix and water sparingly until it roots. Established clumps can also be divided at repotting time. Fresh seed germinates readily where available. See Propagation — cuttings and Propagation — seed for detail.
See also
- Stapelia · Huernia · Apteranthes · Monolluma · Desmidorchis — related stapeliad genera
- Soil and potting mix · Watering · Repotting · Propagation — cuttings · Pests and diseases