Pachypodium horombense
| Light | Bright light to full sun; strongest colour and form in maximum light |
|---|---|
| Water | Regularly while in leaf and growing; keep dry when leafless and dormant |
| Soil | Very free-draining mineral mix (see Soil and potting mix) |
| Temperature | Warm; keep above about 10 °C, no frost |
| Propagation | Seed (primary); grafting occasionally used |
| Toxicity | Sap of the Apocynaceae is generally considered toxic if ingested; keep away from curious pets and children |
Pachypodium horombense is a small caudiciform succulent from the highlands of southern Madagascar, grown for its swollen, bottle-shaped trunk and its cheerful yellow flowers. The blooms are carried well above the plant on long, slender stalks, and each has a distinctively swollen, inflated calyx at its base — a feature that helps separate this species from its close relatives. It belongs to the genus Pachypodium, the "elephant's foot" plants of the dogbane family Apocynaceae.
Description
Pachypodium horombense forms a squat, silvery-grey caudex — a water-storing trunk — that is broadest near the base and tapers upward, giving it the classic bottle or club shape prized by caudiciform collectors. From the top of this trunk arise a few short, spiny branches bearing spines in pairs, and the growing tips carry rosettes of small, oval green leaves during the active season.
The plant is deciduous in the succulent sense: it leafs out in the warm growing months and drops its foliage to rest when conditions turn cool or dry. Its flowers are its signature feature — bright yellow and borne singly or in small clusters on notably long peduncles that lift the blooms clear of the spiny crown. Beneath each corolla sits a conspicuously inflated, balloon-like calyx, an easy field mark for the species.
Distribution and habitat
The species is endemic to southern Madagascar, where it grows on rocky, often granitic outcrops and in gritty, sharply drained ground in a seasonally dry climate. In habitat it endures a pronounced dry season, drawing on the water reserves stored in its caudex, and receives strong sunlight for much of the year.
Like all members of the genus, wild Pachypodium are protected: the entire genus Pachypodium is listed under CITES, and populations can be pressured by collection and habitat change. Nursery-raised, seed-grown plants are the responsible way to grow this species; wild collection is neither legal nor sustainable.
Cultivation
Pachypodium horombense is a rewarding, sculptural plant that asks mainly for warmth, sun and sharp drainage. Grow it in a very free-draining, mostly mineral mix in a pot with generous drainage, and give it the brightest position you can — full sun suits it and keeps the caudex compact and the plant in character.
Water follows the plant's rhythm rather than the calendar. While it is in leaf and actively growing, water thoroughly and then let the mix dry before watering again. As the plant slows and begins to drop its leaves, taper watering off and keep it largely dry through its cool, leafless rest; a wet, cold, dormant caudex is the quickest route to rot. Feed lightly during the growing season only. See Watering and Repotting for general technique.
Propagation
Seed is by far the most reliable method. Fresh seed sown onto a warm, gritty, humid surface germinates well, and seedlings develop their swollen caudex over time. The species does not readily produce offsets, so vegetative increase is uncommon; where a particular plant needs to be reproduced, grafting is occasionally used, though most growers simply raise plants from seed. See Propagation — seed for a full walkthrough.
Common problems
- Rot — the usual cause of loss, almost always from watering a cool or dormant plant, or from a mix that holds moisture too long; the caudex softens and discolours.
- Etiolation — too little light produces weak, stretched growth and a poorly formed caudex; give it as much sun as you can.
- Pests — mealybugs (white fluff at the leaf axils and spine bases) and spider mites in hot, dry, still air are the most common; see Pests and diseases.
See also
- Pachypodium — the genus overview
- Grafting · Soil and potting mix · Watering · Repotting · Propagation — seed · Pests and diseases