Described in 1893 by (T.Mitch. ex Lindl.) K.Schum., this Malvaceae caudiciform is endemic to central Queensland, Australia. As the English common name "Queensland bottle tree" suggests, mature trees reach 10–20 m with a trunk that swells dramatically into a bottle shape — the defining feature of the species. The epithet rupestris means "of the rocks", a nod to the stony hilltop and ridge soils where it grows. Leaves vary strikingly: juvenile foliage is deeply lobed and compound, adult leaves narrow and lance-shaped. Drought-deciduous, tough, and faster-growing than most caudex plants, it has become a staple species for caudex beginners.
Native climate
Rainfall is spread fairly evenly across the year. Overall mild, with a wide temperature range.
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
In central Queensland's hill country it grows in unshaded full sun, so give it all-day direct light when in growth. Outdoors through the active season the trunk thickens and the leaves stay short and tight. It tolerates Japan's harsh midsummer better than most caudex plants, but raise the pot off the ground on a bench for airflow to keep root rot at bay. As leaves drop heading into dormancy, taper water and bring it to a bright window kept above 5°C. Never leave it out in frost.
Watering
In active growth, water deeply once the surface dries and let the trunk store moisture; never leave water in the saucer. Once leaves drop, taper sharply and overwinter dry, perhaps a small drink once or twice a month.
Substrate
Drainage first, inorganic-led: Akadama : Kanuma : pumice = 4:3:3 as the base. A deeper pot with sharp wet/dry cycles thickens the trunk cleanly.
Fertilizer & Supplements
Diluted liquid feed once or twice a month in active growth, or a pinch of slow-release at repotting. This species grows fast and fattens quickly with a moderate dose; overfeeding only causes etiolation.
Temperature & Overwintering
Optimal 22–32°C, 5°C minimum. One of the more cold-tolerant in the genus, but a single night of frost will scar the trunk. Bring it in early once leaves drop and overwinter dry on a bright window.
Starting from Seed
Where to source seeds
Pre-sowing treatment
The pod's hairs are skin-irritating, so wear gloves when extracting. 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. The hard coat takes time to imbibe evenly.
Substrate
Fine-grained, near-sterile seedling mix: fine Akadama, fine Kanuma, vermiculite at 1:1:1. Sterilize with boiling water or a microwave pass to head off damping-off.
Sowing method
Seeds are mid-sized (5–8 mm). Press lightly into the surface and cover with about 5 mm. Space at least 2 cm apart to avoid crowding.
Light & temperature
Bright shade, holding 25–30°C steady. Expect germination in 7–21 days. Germination depends strongly on seed freshness, but fresh seed tends to come up well.
Watering
Bottom-water with the level 1–2 cm up the pot. Don't let things dry for the first 2–3 weeks; once germination is even, drop the level in stages.
Fertilizer
No feeding right after germination. Once true leaves emerge, a diluted liquid feed once or twice a month. Growth is fast enough that the trunk starts thickening in the first year on a moderate dose.
From Germination to Repotting
Germination through true leaves
Continue bottom watering, avoid strong light.
Weaning off bottom watering
Step down gradually over 1–2 months.
First repotting
In the first year, once root-bound.
Common Pitfalls
Mold & damping-off
- Cause: excess moisture, contamination, poor air flow
- Prevention: sterilize substrate, change bottom water frequently
Etiolation
- Cause: insufficient light
- Prevention: bring LEDs closer right after germination, or move to bright outdoor light
Seeds fail to germinate
- Cause: stale seed, insufficient warmth
- Prevention: fresh seed and 25–30°C on a heat mat
Notes
The hairs around the seeds irritate skin — wear gloves when handling.
