A shrubby Alluaudia from the spiny thicket of southwestern Madagascar. Described by Choux in 1934, the specific epithet honours the French botanist Henri Humbert, the foremost student of the Madagascan flora. Unlike the tall columnar A. procera or A. ascendens, this is the genus's shrub: a short trunk branches close to the ground, and slender spiny shoots arch outward in a low, spreading crown. Small fleshy round leaves emerge between paired spines along the stems. Old specimens reach 4–6 m, but in cultivation the plant stays manageable at decimeters to a meter or so for many years — a quietly collector-favoured species for those willing to take their time.
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
Adapted to the strong sun and severe dryness of southwestern Madagascar, this species wants full direct sun outdoors through the active season. Insufficient light produces stretched, soft shoots that lose the species' compact, woody character. Through Japan's midsummer, light shading at 20–30% with the pot raised on a bench for airflow is the safer setting. Overwinter on a bright sunny window kept above 8°C and bone-dry.
Watering
In active growth, water thoroughly once the substrate is fully dry, then dry it back quickly with good airflow. Habitat receives only a few hundred millimeters of rain a year — the plant resents lingering wetness. Taper through autumn and go essentially dry through winter.
Substrate
Drainage first, inorganic-led. Akadama : Kanuma : pumice = 4:3:3. Sift out fines, use a deeper pot, and ensure generous drainage holes.
Fertilizer & Supplements
A small pinch of slow-release at repotting, or liquid feed at double dilution once a month in active growth. Excess nitrogen stretches the shoots and erodes the short, woody form that defines the species.
Temperature & Overwintering
Optimal 22–35°C, minimum 8°C — about as hardy to cold as A. procera. Below ~5°C shoot tips blacken. Damp soil + cold is the fast way to lose the plant — winter dryness sets up a clean spring start.
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. Floaters are typically past their prime — common with this species, where stock reaches the trade in small batches and is often not freshly harvested.
Substrate
Use a separate seedling mix that's fine-grained and near-sterile: fine Akadama, fine Kanuma, and vermiculite in 1:1:1 parts. A boiling-water or microwave pass beforehand cuts damping-off.
Sowing method
Sow with no covering, or only the thinnest dusting of substrate so the seeds remain partly visible. Space the seeds at least 1 cm apart so they don't clump or overlap on the surface.
Light & temperature
Bright shade, 25–30°C. Germination typically lands within 10–30 days, but stragglers are common — keep the heat steady on a heat mat and stay patient.
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 level gradually once seedlings are stable.
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, in bright shade.
Weaning off bottom watering
Phase it out gradually over 1–2 months.
First repotting
In the first or second year, 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
- Prevention: source from reliable sellers, prioritize fresh seed, and hold 25–30°C steady on a heat mat
Notes
The spines are short but genuinely sharp, paired at the base of each leaf — wear thick gloves and keep the plant out of high-traffic zones with children or pets. The Didiereaceae have been on CITES Appendix II since 1977, so source from reputable, properly documented sellers.
