A small cactus from the Moctezuma River canyon along the Hidalgo–Querétaro border in Mexico, where it lives half-buried in the cracks of near-vertical limestone cliffs. The Japanese name is "Kikusui" (菊水). The flattened, disc-like body carries small tubercles arranged in a spiral — an exceptionally slow grower that reaches only 3–5 cm across after a decade from seed. The accepted name in POWO is Strombocactus disciformis (DC.) Britton & Rose; the original description was Mammillaria disciformis DC. (1828), transferred to Strombocactus by Britton & Rose in 1922. IUCN: Vulnerable. CITES: Appendix I. The genus comprises just this species and S. corregidorae S.Arias & E.Sánchez (2010); two subspecies, subsp. disciformis and subsp. esperanzae, are recognised within S. disciformis.
Native climate
Rain concentrates in the warm season, with a dry season of roughly 5 months. 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
Grows in the cracks of limestone cliffs in the Moctezuma River canyon at 1,000–1,600 m, in the partial shade of vertical rock walls — strong direct light browns the epidermis. Through the growing season, give it bright partial shade outdoors, or a spot with only morning sun; all-day direct exposure is best avoided. In Japan's hot midsummer, 30–40% shade and a raised bench for airflow are sensible, and a circulator helps. In winter dormancy, move it to a bright, unheated indoor window kept above 5°C and hold it nearly dry.
Watering
Through active growth, water thoroughly once the substrate is fully dry, then let it dry well again. Slow growth means low water use, so excess moisture is poorly tolerated. In dormancy, keep it nearly dry — a light misting once or twice a month is enough.
Substrate
Drainage first, inorganic-led: Akadama : Kanuma : pumice = 3:3:4 as a base. Because it grows on limestone, adding a small amount of crushed oyster shell or dolomitic lime to the mix is worthwhile. Use a deep pot to let the taproot extend.
Fertilizer & Supplements
Dilute liquid feed once a month in active growth, mixed weaker than the label rate. As a slow-growing species, overfeeding causes epidermal splitting and stretched growth. A pinch of slow-release at repotting is enough.
Temperature & Overwintering
Optimal 18–30°C, 5°C minimum. As a highland species it is sensitive to heat and humidity combined; in midsummer tropical nights, support it with shade and airflow. Overwinter dry — wet soil under cold is fatal. Slow growth means repotting every 2–3 years is sufficient.
Starting from Seed
Where to source seeds
Pre-sowing treatment
The seeds are roughly 0.3 mm — dust-fine — and are sprinkled dry directly onto the substrate surface. A pre-soak is impractical at this size; instead, use a registered seed-treatment fungicide (Benlate or Daconil; outside Japan, a captan- or thiram-based product works similarly) together with a plant tonic (Menedael; SUPERthrive or a dilute seaweed/chelated-iron solution as an analogue) in the bottom-water tray. Sow as soon as the packet arrives, since viability fades quickly.
Substrate
Fine-grained and near-sterile: fine Akadama, vermiculite, and fine pumice at roughly 2:1:1 — enough moisture retention for dust-fine seedlings, with airflow underneath. Sterilize with boiling water or a microwave pass to head off damping-off.
Sowing method
Because the seeds are tiny, no covering at all — just dust them onto the surface. Spacing them one at a time with a toothpick tip makes later management easier. A clear lid or plastic wrap keeps humidity in.
Light & temperature
Bright shade at 22–28°C. Germination is quick, with most seeds breaking ground in 7–21 days. Germination depends strongly on seed freshness; even with fresh seed, germination rates tend to be on the modest side.
Watering
Bottom-water with the level 1–2 cm up the pot. With seeds this small, the priority for the first one to two months is never letting the substrate dry out — a clear lid to hold humidity helps.
Fertilizer
No feeding right after germination. Once secondary areoles — the equivalent of true leaves for a cactus — begin to show, give heavily diluted liquid feed about once a month. As a slow-growing species, overfeeding is best avoided.
From Germination to Repotting
Germination through true leaves
Continue bottom watering, avoid strong light.
Weaning off bottom watering
Transition gradually over 2–3 months.
First repotting
In the second or third year, once the roots have filled the pot.
Common Pitfalls
Mold & damping-off
- Cause: excess moisture, contamination, dust-fine seed buried by water
- Prevention: sterilize substrate, surface-sow without covering, refresh bottom water often
Epidermal scorch from strong light
- Cause: sudden direct sun, summer heat combined with strong light
- Prevention: keep in partial shade, add 30–40% shade cloth in summer
Seeds fail to germinate
- Cause: stale seed, insufficient warmth
- Prevention: fresh seed and 22–28°C on a heat mat
Stalled growth or rot
- Cause: excess moisture, planting too deep, overfeeding
- Prevention: clear wet–dry cycles, keep the neck of the plant exposed, feed sparingly
Notes
Trade in wild-collected plants is prohibited under CITES Appendix I.