Uncarina is a genus of the Pedaliaceae family comprising 11 species, all of them endemic to Madagascar. Found exclusively in the island’s arid south and west — one of the planet’s most remarkable botanical regions — these plants have evolved a striking pachycaul growth form in response to the extreme seasonality and periodic drought that characterise their native habitat. With their swollen stems, spectacular flowers, and extraordinary hooked fruits, Uncarina species occupy a unique position in the world of succulent plants.
Morphology and growth form
Each Uncarina develops a thick, swollen caudex at the base — a water-storing organ that allows the plant to survive the long dry season that dominates Madagascar’s southern interior. From this caudex, the plant produces annual or semi-annual stems bearing large, roughly textured leaves, attractive to the touch and subtly viscous in texture due to the mucilaginous coating characteristic of the family. As the dry season approaches, these stems die back, leaving the bare caudex to weather the drought in dormancy.
The flowers of Uncarina are among the most spectacular produced by any pachycaul plant. Large and funnel-shaped, they are borne freely during the growing season in shades of bright yellow or delicate pink, often with a deeper-coloured throat. Each flower lasts only a day or two, but the plant produces blooms in succession over several weeks, creating a prolonged and vivid display quite unexpected in a plant adapted to drought.
The hooked fruits
The fruits of Uncarina are among the most memorable structures in the plant kingdom. Woody and dry at maturity, they are densely armoured with hooked spines that grip the fur, feathers, or skin of any passing animal with extraordinary tenacity — including, as collectors soon discover, human skin and clothing. This mechanism, known as epizoochory, evolved in concert with the large mammals that once roamed Madagascar, including giant lemurs and possibly even the now-extinct elephant bird. The fruits can inflict painful wounds and should be handled with care.
Key species
Uncarina roeoesliana — one of the most frequently cultivated species, producing large, bright yellow flowers with an attractive orange-red throat. The caudex develops well in cultivation and the plant blooms reliably when given sufficient warmth and light. Considered one of the best species to begin with for collectors new to the genus.
Uncarina grandidieri — a larger species capable of developing an impressive caudex, named in honour of the French naturalist Alfred Grandidier. It produces pale yellow flowers and is one of the more robust species in cultivation, tolerating brief periods of neglect better than some of its relatives. Its fruits are particularly formidable.
Uncarina stellulifera — distinguished by its delicate, star-patterned flower markings in the throat, this species is among the more sought-after in specialist collections. It tends to grow somewhat more slowly than U. roeoesliana but rewards patience with characterful caudex development and distinctive blooms.
Cultivation
Uncarina requires full sun, warmth, and a sharply draining substrate. A mix of grit, perlite, and a small proportion of organic matter suits most species. Water freely during the growing season (spring and summer) and reduce to virtually nothing during winter dormancy; the caudex should not be kept completely dry for extended periods, but overwatering when dormant is fatal. A minimum winter temperature of 12°C is recommended for most species; they are not frost-tolerant.
Repotting is best carried out at the start of the growing season. Propagation is from seed, which germinates readily in warm, moist conditions. Handle mature fruits with gloves — the hooked spines are no metaphor.