A medium-sized caudex from northwestern Madagascar, native to the dry forests around Mahajanga. Authority is Humbert ex Ihlenf., with the specific epithet honouring Raymond Decary, a pioneering botanist of the Madagascan flora. Mature plants reach 2–3 m, smaller and more compact than U. grandidieri, with heart-shaped lobed leaves that often carry a red petiole — a useful field mark distinguishing it from grandidieri. Bright yellow 5-petalled flowers with a dark purple-black throat appear in summer, followed in autumn by the genus's signature hooked seed pods. Together with grandidieri it is one of the two main Uncarina in cultivation, robust and well suited to pot growing — a good entry point for seed-grown caudex.
Native climate
Rain concentrates in the warm season, with a distinct dry season. Overall a warm climate.
A broad-scale picture of the native range. Real growing spots — rock crevices, fog belts — can be milder.
Sources: climate & elevation WorldClim 2.1 (1970–2000) · occurrences GBIF · native range POWO · current weather Open-Meteo
Care
Light & Placement
A summer-grower from the dry deciduous forest around Mahajanga, exposed to strong sun and a hard dry season. Full direct sun outdoors during the growing season keeps the compact form tight, with deep-coloured, fully expanded leaves. A 20–30% shade cloth helps through Japan's worst midsummer; raise pots off the ground for airflow. Overwinter on a bright sunny window kept above 8°C and dry, sheltered from rain.
Watering
In active growth, water deeply once the substrate has dried, then dry it out fully again. This species is the easier of the two main Uncarina on the watering side, but as with grandidieri, pushing too much water elongates branches. Taper as autumn cools, then go nearly dry through winter, with at most a single light misting per month.
Substrate
Drainage first, inorganic-led. Akadama : Kanuma : pumice = 4:3:3 is reliable. The species suits a slightly shallower pot than grandidieri thanks to its compact habit, but a deep pot still encourages caudex thickening.
Fertilizer & Supplements
A diluted liquid fertilizer monthly through active growth, or a small pinch of slow-release at repotting. The species responds steadily to modest feeding and is easy to keep in shape — no need to push the dose.
Temperature & Overwintering
Optimal 22–35°C with an 8°C minimum. As a Madagascan species it is cold-sensitive — branch tips suffer below 5°C, and damp soil with cold is fatal. As autumn cools and leaves drop, taper water early and overwinter on a bright indoor window, holding the dry-warm rhythm until spring.
Starting from Seed
Where to source seeds
Pre-sowing treatment
Soak seeds for about half a day (overnight) in a mix of a registered seed-treatment fungicide (Benlate or Daconil) and a plant tonic (Menedael; outside Japan, SUPERthrive or a chelated iron / seaweed extract works similarly), each diluted per label. Any that stay afloat are likely past their prime. The seed coat is hard, typical of Pedaliaceae — light scarification (gentle abrasion with sandpaper) improves water uptake.
Substrate
Use a separate seedling mix that's fine-grained and near-sterile: fine Akadama, fine Kanuma, and vermiculite in 1:1:1 parts. Sterilizing beforehand reduces damping-off.
Sowing method
Sow with no covering, or only the thinnest dusting so the seeds remain partly visible. Space at least 1 cm apart.
Light & temperature
Bright shade, 25–30°C steady. Germination spreads over 10–30 days and is generally even on a heat mat.
Watering
Bottom-water with the level 1–2 cm up the pot. For the first 2–3 weeks, prioritize not letting things dry out, then drop the water level gradually.
Fertilizer
No feeding right after germination. Once true leaves emerge, give diluted liquid fertilizer at double dilution, once or twice a month.
From Germination to Repotting
Germination through true leaves
Continue bottom watering, keep strong light off them.
Weaning off bottom watering
Phase out gradually over 1–2 months.
First repotting
In year one or two, once roots have filled the pot.
Common Pitfalls
Mold & damping-off
- Cause: excess moisture, contamination, poor air flow
- Prevention: sterilize the substrate, refresh the bottom-water, and use a circulation fan
Etiolation
- Cause: insufficient light
- Prevention: move LEDs closer right after germination, or shift the tray to bright shade outdoors
Seeds fail to germinate
- Cause: stale seed, insufficient warmth, hard seed coat blocking water uptake
- Prevention: source fresh seed, lightly scarify before soaking, hold 25–30°C steady on a heat mat
Notes
Mature fruits carry sharp hooks that grip clothing and fingers tenaciously. Use leather gloves when pruning or harvesting seed, and keep harvested pods away from pets and small children.
