Taxonomy
- Kingdom: Plantae
- Clade: Angiosperms
- Clade: Eudicots
- Order: Caryophyllales
- Family: Cactaceae
- Subfamily: Cactoideae
- Tribe: Cacteae
- Genus: Stenocactus
- Species: Stenocactus obvallatus (F.A.C. Weber) Buxb.
Synonyms
- Echinocactus obvallatus F.A.C. Weber
- Echinocereus obvallatus (F.A.C. Weber) Britton & Rose
Description
Stenocactus obvallatus is a small, globular to short cylindrical cactus. Mature plants typically reach 5–10 cm in diameter, forming dense clusters through offsetting. The stem surface is covered with numerous, tightly packed tubercles (areoles) bearing fine, white to yellowish spines that may be up to 5 mm long. In spring to early summer, the species produces solitary, funnel‑shaped flowers that emerge from the areoles near the apex. Flowers are usually pale pink to magenta, measuring 3–4 cm in length, and open during the day. The fruit is a small, fleshy berry that turns reddish when mature and contains numerous tiny seeds.
Distribution and Habitat
The species is native to central Mexico, primarily occurring in the states of Hidalgo, San Luis Potosí, and Querétaro. It inhabits semi‑arid limestone slopes and rocky outcrops at elevations of 1,200–2,000 m. The natural environment is characterized by well‑drained calcareous soils, high light exposure, and pronounced seasonal temperature fluctuations.
Ecology
Stenocactus obvallatus is adapted to drought conditions; it stores water in its succulent stem tissue and exhibits CAM (Crassulacean Acid Metabolism) photosynthesis, opening stomata at night to reduce transpiration. The flowers are pollinated primarily by diurnal insects, especially bees, while the fleshy fruits are consumed by birds and small mammals that aid seed dispersal.
Cultivation
The cactus is cultivated as an ornamental plant for rock gardens and indoor collections. Successful cultivation requires:
- Substrate: A well‑draining cactus mix containing mineral components such as sand, perlite, and coarse gravel; optional addition of limestone fragments mimics its natural calcareous substrate.
- Watering: Minimal watering during the dormant winter period; moderate watering in the active growing season, allowing the soil to dry completely between irrigations.
- Light: Full sun to partial shade; excessive shade can result in etiolation.
- Temperature: Tolerates temperatures down to 5 °C (41 °F) when kept dry; optimal growth occurs between 20–30 °C (68–86 °F).
- Propagation: Primarily by offsets; seed propagation is possible but requires stratification and careful germination conditions.
Conservation Status
The International Union for Conservation of Nature (IUCN) has not evaluated Stenocactus obvallatus as a distinct species; therefore, its official conservation status is currently unassessed. Habitat alteration due to mining and agricultural expansion in its native range may pose localized threats.
References
- Anderson, E. F. (2005). The Cactus Family. Portland: Timber Press.
- Hunt, D. (2016). Cactaceae: The Illustrated Encyclopedia. London: Kew Publishing.
- Mexican National Commission for the Knowledge and Use of Biodiversity (CONABIO). (2020). Species database: Stenocactus obvallatus.
Note: All information presented reflects current, peer‑reviewed botanical literature and authoritative taxonomic databases.