Jatropha
Jatropha is a genus of flowering plants in the spurge family Euphorbiaceae, containing well over a hundred species of shrubs, small trees and herbaceous perennials from the warmer regions of the Americas, Africa and Asia. Among succulent collectors the genus is prized for a handful of caudiciform species that build a swollen, water-storing stem or underground tuber (a caudex), topped with lobed leaves and clusters of bright, long-lasting flowers. As with other spurges the sap is irritant and the seeds are poisonous, so the group is grown strictly as an ornamental curiosity.
Description
The succulent members of Jatropha share a distinctive habit: a fat, often bottle- or turnip-shaped caudex — sometimes held above ground, sometimes buried like a tuber — that stores water and carries the plant through long dry seasons. From this base rise soft, deciduous stems bearing large, palmately lobed or divided leaves that are shed in the dormant period.
The flowers are a highlight. Small individually, they are carried in branched clusters on tall stalks, most often in shades of coral, scarlet or pink, and many species bloom over a long season. Plants are typically monoecious, with separate male and female flowers in the same cluster. Like other euphorbs, Jatropha produces a latex when cut — in this genus usually thin and watery rather than the copious white sap of many relatives — and the three-chambered seed capsules split explosively to scatter their seeds.
Distribution
The genus is centred on the tropical and subtropical Americas, with a strong secondary presence in Africa and Madagascar and scattered species across Asia. The succulent, caudex-forming species tend to come from seasonally dry habitats — thornscrub, rocky slopes and open savanna — where the swollen stem is an adaptation to a pronounced wet-and-dry climate. Several non-succulent species, notably Jatropha curcas, have been spread far beyond their native range as hedge, oilseed and medicinal plants and are now widely naturalised in the tropics.
Notable species
- Jatropha podagrica — the Buddha belly plant or gout stalk; the most commonly grown caudiciform, with a knobbly, bottle-shaped grey stem and long-stalked heads of coral-red flowers. An excellent beginner's caudex plant.
- Jatropha cathartica (often sold as Jatropha berlandieri) — a Texan and Mexican species forming a rounded underground tuber that growers usually raise partly above the soil to show it off.
- Jatropha multifida — the coral plant, a taller, less strongly caudiciform species with finely dissected leaves and flat-topped clusters of vivid coral flowers.
- Jatropha curcas — the physic nut or Barbados nut, a shrubby, non-succulent species grown historically as a hedge and biofuel oilseed; notable mainly for its toxicity and economic history rather than as a collector plant.
Cultivation
The caudiciform species are grown much like other tropical caudex plants: give them plenty of warmth, strong light and a very free-draining, mostly mineral mix. They are actively growing plants during the warm months — water thoroughly once the mix has dried, and enjoy the leaves and flowers through the season.
The key to success is respecting their dormancy. As days shorten and temperatures fall the plants naturally drop their leaves; at this point reduce watering sharply and keep them warm and nearly dry until growth resumes in spring. Overwatering a leafless, dormant plant is the fastest way to rot the caudex. Keep them frost-free at all times — they are tender and best treated as houseplants or greenhouse subjects outside the true tropics. See Watering, Repotting and Pests and diseases for general technique.
Toxicity note: every part of a Jatropha is poisonous if eaten, the seeds especially so, and the sap can irritate skin and eyes. Wash your hands after handling or pruning, keep the plants away from children and pets, and treat any cut surface with care.
In cultivation
Jatropha has not been bred into the sprawling cultivar groups seen in some succulent genera; hobby interest centres on the natural species and on well-grown, characterful caudices rather than named clones. Plants are almost always raised from seed (see Propagation — seed), which germinates readily when fresh and warm and quickly begins to swell at the base. Cuttings can be rooted from some species (see Propagation — cuttings) but generally produce a less shapely, less pronounced caudex than seed-grown plants, so seed remains the preferred route for a good specimen. A few growers graft or raise unusual forms, but the genus is valued above all for the sculptural appeal of a mature, fat-stemmed plant in full coral bloom.
See also
- Euphorbiaceae — the spurge family
- Caudex · Caudiciform plants
- Soil and potting mix · Watering · Repotting · Propagation — seed · Propagation — cuttings · Pests and diseases