A narrowly distributed Alluaudia from the Mahafaly Plateau of southwestern Madagascar, restricted to a thin coastal strip near Itampolo and rare in cultivation. Described by Werner Rauh in Adansonia in 1961, the specific epithet honours the French collector M.R. Montagnac. Recognised by a columnar central trunk with strong vertical branches, sharply pointed black-tipped spines 2–2.5 cm long that are always longer than the leaves, and small dark-green leaves around 1.5 cm set between them. Compared with A. procera, the spines are denser and longer and the leaves are smaller and darker. IUCN-listed Endangered, with only 2–5 known locations at 0–500 m elevation. Limited stock and growing notes place it in the mid-to-advanced bracket rather than the entry point of the genus.
Native climate
Rain concentrates in the warm season, with a distinct dry season. Overall a warm climate.
* Accurate distribution data is scarce for this species, so these values are taken from the climate near the approximate center of its native range instead.
Sources: climate & elevation WorldClim 2.1 (1970–2000) · occurrences GBIF · native range POWO · current weather Open-Meteo
Care
Light & Placement
In the sandy and limestone-derived spiny forest of Mahafaly this species grows in unrelenting direct sun, so give it as much full light as possible during active growth. Most plants in circulation are smaller saplings with limited root systems, so step them gradually into the strongest summer sun. 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 dry.
Watering
In active growth, water deeply once the substrate has dried completely, then dry it out fully again. A touch more sensitive to overwatering than procera. Taper through autumn and go dry through winter.
Substrate
A sharply draining inorganic mix is essential. Akadama : Kanuma : pumice = 4:3:3, with a slightly higher pumice fraction than for procera if you want to dry the pot out faster. Deep pot, generous drainage holes.
Fertilizer & Supplements
A diluted liquid fertilizer monthly in active growth, or a small pinch of slow-release at repotting. Response to feeding is more muted than procera — pushing the dose mainly stretches internodes. Keep doses modest.
Temperature & Overwintering
Optimal 22–35°C, minimum 8°C. Bone-dry plants tolerate brief drops near 5°C, but damp soil below ~10°C rots the trunk fast — go fully dry before bringing indoors.
Starting from Seed
Where to source seeds
links go directly to the product page; the rest are scientific-name searches. Stock fluctuates — verify availability on the destination site.
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. Seeds left floating tend to be past their prime, which isn't unusual given that stock is unusually thin even within the genus.
Substrate
Use a separate seedling mix that's fine-grained and near-sterile: fine Akadama, fine Kanuma, and vermiculite in 1:1:1 parts. Sterilize beforehand — seedlings seem more prone to damping-off than procera.
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. Some seeds break ground around 10 days, but a full flush can take close to a month. Germination depends heavily on seed freshness, and even fresh seed stays on the lower side.
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 open, give diluted liquid fertilizer at double dilution or weaker, 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 unusually long (2–2.5 cm), dense, and hard-tipped — use thick leather gloves and tongs when handling. Listed as Endangered on the IUCN Red List, with only 2–5 known subpopulations on the Mahafaly Plateau. The Didiereaceae are on CITES Appendix II, so confirm the chain of custody and import paperwork when buying a live specimen.
