A cactus of extremely narrow range, found only on a few square kilometres of gypsum cliff in Nuevo León, Mexico. A relatively recent species described in 2013 by Velazco, Alvarado and Arias, it was named for the biologist Mario Valdéz, who found it. At just 2–6 cm tall it is among the smallest of the genus. The precise locality is withheld for its protection. POWO accepts it as a distinct species, whereas Hunt (2016) treats it as falling within the variation of A. ritteri; CITES follows that view and places it in the same Appendix I listing as A. ritteri. Being so newly described, it has not been assessed by the IUCN. Cliff erosion and illegal collection are the main threats.
Native climate
Rain concentrates in the warm season, with a dry season of roughly 6 months. Overall mild, at high elevation, 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 eroding gypsum cliffs in Nuevo León, on steep faces where strong light readily browns 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 exceptionally slow and water uptake very 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 so slow a species, overfeeding leads to etiolation and splitting of the body. A small pinch of slow-release granules at repotting is enough.
Temperature & Overwintering
Optimal 18–30°C, with 5°C as the minimum guide. 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 about once every 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 takes about 14–30 days. Germination depends heavily on seed freshness, and even fresh seed remains inconsistent — among the harder species.
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 so slow a species, 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 three to six months.
First repotting
After year 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 under CITES Appendix I as a rare species: international trade in wild plants is prohibited.
