A small cactus of a monotypic genus — one genus, one species — found only on gypsum cliffs near Galeana in Nuevo León, Mexico. George Hinton came upon it in 1991, and Glass and Fitz Maurice described it the following year. The blue-green, globose to slightly columnar body carries deep ribs lined with white wool and bears small pink flowers at the crown. It shares its cliffs with Aztekium hintonii. The POWO accepted name is Geohintonia mexicana (1992); the IUCN rates it Near Threatened; and it is listed on CITES Appendix II.
Native climate
Rain concentrates in the warm season, with a dry season of roughly 6 months. Overall mild, with a wide temperature range, and cold winters.
* 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 habitat this species grows on gypsum cliffs in Nuevo León at 1,200–1,350 m, taking full light on steep faces, yet Japan's midsummer sun can scorch the epidermis. During the growing season a bright semi-shade outdoors — or a position with direct sun only in the morning — suits it well; avoid all-day strong sun. Through high summer, 30–40% shade cloth with good air circulation on a raised bench is the safe approach, and a circulator helps. For winter dormancy, bring it inside to a bright, sunny window, keep it above 5°C, and manage on the dry side.
Watering
During the growing season, water thoroughly once the substrate has dried completely, then let it dry again — that wet-dry rhythm matters. Growth is slow and water uptake low, so it dislikes prolonged moisture. In dormancy, hold back and limit to a light misting once or twice a month.
Substrate
Prioritise drainage with a mostly inorganic mix. A base of small-grain Akadama : Kanuma : pumice = 3:3:4 works well; echoing its gypsum habitat, a little crushed oyster shell or dolomitic lime is worth adding. A deep pot lets the taproot develop.
Fertilizer & Supplements
A dilute liquid feed once a month in the growing season, well past twice the label dilution and kept light. In a slow-growing species, overfeeding leads to etiolation and distorted ribs. A small pinch of slow-release granules at repotting is enough.
Temperature & Overwintering
Optimal 18–30°C, with 5°C as the minimum guide. A highland plant, it dislikes hot, humid conditions; support it through tropical nights with shade and airflow. Overwinter dry — damp plus cold is fatal. Given the slow growth, repotting every two to three years is plenty.
Starting from Seed
Where to source seeds
Pre-sowing treatment
Seeds are tiny, around 0.5 mm, and are scattered dry onto the surface. Bottom water should carry a registered fungicide (Benlate or Daconil 1000 at label dilution) with a tonic such as Menedael. Storage affects freshness, so sow as soon as possible after receipt.
Substrate
For seedlings, a fine-grained, near-sterile mix: fine Akadama : vermiculite : fine pumice = 2:1:1, sterilised with boiling water or a microwave pass.
Sowing method
Because the seeds are so small, no covering is used — scatter them directly onto the surface. Spacing them one by one with a toothpick tip eases later care. Hold humidity with a transparent lid or wrap.
Light & temperature
Maintain bright shade at 22–28°C. Germination evens out over about 7–21 days. Germination depends heavily on seed freshness, and even fresh seed stays on the lower side.
Watering
Bottom-water at 1–2 cm up the pot. As the seeds are minute and dry out easily, keeping the substrate from drying is the priority for the first one to two months. A transparent lid helps hold humidity.
Fertilizer
No feeding right after germination. Once secondary areoles appear, a heavily diluted liquid feed once a month, kept very light. In a slow grower, overfeeding is to be avoided.
From Germination to Repotting
Germination through true leaves
Continue bottom watering; avoid strong light.
Weaning off bottom watering
Reduce gradually over two to three months.
First repotting
In year two or three, once the roots have filled the pot.
Common Pitfalls
Mold & damping-off
- Cause: excess moisture, contamination, tiny seeds becoming buried
- Prevention: sterilise substrate, sow without covering, change bottom water frequently
Etiolation & rib elongation
- Cause: insufficient light, overfeeding
- Prevention: keep in bright semi-shade; dilute fertiliser well beyond the label rate
Seeds fail to germinate
- Cause: old seed, insufficient temperature
- Prevention: choose legally sourced fresh seed; hold 22–28°C with a heat mat
Epidermal scorch
- Cause: abrupt strong light, combined summer heat and intense sun
- Prevention: manage in semi-shade; add 30–40% shade cloth in high summer
Stalled growth or rot
- Cause: excess moisture, planting too deep, overfeeding
- Prevention: keep a clear wet-dry rhythm; avoid burying the crown; keep feeding minimal
Notes
Listed on CITES Appendix II: collection and trade of wild plants are regulated.