Pachypodium
Pachypodium is a genus of spiny, caudiciform succulent trees and shrubs in the dogbane family Apocynaceae, native to Madagascar and southern Africa. Its members combine swollen, water-storing trunks and stems with sharp, often paired spines, and range from squat, boulder-like dwarfs a few centimetres across to slender columnar "palms" several metres tall. The name means "thick foot", a nod to the fat, fleshy caudex that defines the group, and the genus is a close relative of the desert rose Adenium.
Description
Pachypodium species share a distinctive combination of succulence and armament. The trunk or stem is thickened into a water-storing body — sometimes a low, flattened dome, sometimes a tapering bottle or column — with a firm, often silvery or greyish skin. From the spine-bearing areole-like nodes emerge spines, usually in twos or threes, that persist as the plant ages and give even leafless specimens a formidable look.
Unlike true cacti, Pachypodium bears proper leaves, generally clustered in a rosette toward the growing tips. Most species are drought-deciduous, dropping their leaves and resting through the dry season. The flowers are typical of the family — five-petalled, salverform blooms in white, cream, yellow, pink or red — and in some species are large and showy, produced at the branch tips. Unlike most of Apocynaceae, whose members bleed a milky latex, Pachypodium has a clear, watery sap; it can nonetheless irritate the skin and eyes, so see Toxicity below.
Distribution
The genus is centred on Madagascar, where the great majority of species occur, many of them narrowly endemic to particular rocky outcrops, granite domes or dry deciduous forests. A smaller group is found on the African mainland, in the arid regions of South Africa, Namibia and neighbouring countries. Across this range the plants favour hot, seasonally dry habitats — exposed rock, gritty slopes and thornscrub — where their swollen bodies buffer them against long droughts.
Several species are of conservation concern, having been over-collected from the wild or squeezed by habitat loss; like many succulents they are covered by CITES trade controls. Nursery-grown, seed-raised plants are widely and legally available, and wild collection is neither necessary nor acceptable.
Notable species
- Pachypodium lamerei — the "Madagascar palm", a tall, spiny column topped with a rosette of strap-like leaves; by far the most common species in cultivation and a forgiving beginner's plant.
- Pachypodium geayi — similar in habit to P. lamerei but with narrower, greyer leaves and a slightly more demanding temperament.
- Pachypodium brevicaule — a prized dwarf that grows as a low, lumpy, grey caudex hugging the ground, studded with tiny leaves and yellow flowers; slow and much sought after.
- Pachypodium namaquanum — the South African "halfmens", a slow, columnar species with a shaggy crown that famously leans toward the equatorial sun.
- Pachypodium rosulatum — a variable species forming a rounded, bottle-shaped caudex with yellow flowers, including the popular Madagascan forms often sold as gracilius.
- Pachypodium saundersii and Pachypodium bispinosum — mainland species with fat, partly buried caudices, well suited to caudex-forward "bonsai" display.
Cultivation
Most Pachypodium are rewarding houseplants and greenhouse subjects, asking for warmth, strong light and restraint with the watering can. Grow them in a very free-draining, mostly mineral mix in a pot that is snug rather than oversized. Give them the brightest position available — full sun for the columnar species — as too little light causes weak, etiolated growth and reluctance to flower.
Watering follows the plants' seasonal rhythm. During active growth in the warm months, water thoroughly once the soil has dried, then let it dry again; taper off as the days shorten. Most species are drought-deciduous and take a dry winter rest, during which they should be kept nearly bone dry and, importantly, warm. Pachypodium resent cold wet roots more than almost anything, and winter overwatering is the classic cause of loss. Keep them above roughly 10–13 °C; the Madagascan species in particular dislike a cold snap. See Watering and Repotting for general technique, and check regularly for pests such as mealybugs and spider mites.
Propagation
Seed is the primary and most satisfactory method for the genus, giving well-shaped plants with a naturally fat caudex. Fresh seed germinates readily on a warm, moist mineral surface, and seedlings grow surprisingly quickly in their first years. Some species branch and can be grown from cuttings, but cutting-grown plants often lack the swollen base that makes the genus so appealing, and they root less reliably than the seed-raised alternative. Grafting is occasionally used for very slow or difficult dwarfs. See Propagation — seed and Propagation — cuttings.
Toxicity
Unlike most of Apocynaceae, Pachypodium does not produce a milky latex; its sap is clear and watery. It can still irritate the skin and eyes, and as a sensible precaution all parts are best treated as inedible. Combined with their sharp spines, this makes them plants to site out of reach of curious children and pets. Wash hands after pruning and avoid getting the sap in the eyes.
Hobby and cultivar notes
In cultivation the tall species — especially P. lamerei — are grown as easy, architectural houseplants, while the fat-bodied dwarfs are collected and displayed much like succulent bonsai, with the caudex raised and shown off. Interspecific hybrids exist and some named clones circulate among specialists, but the genus is grown far more for its wild species and their natural caudex forms than for a large cultivar range. Growers prize individual plants for the character of the caudex, the branching and the flowering.
See also
- Adenium — the closely related desert roses
- Caudex · Soil and potting mix · Watering · Repotting
- Propagation — seed · Propagation — cuttings · Pests and diseases