Origin and Habitat: Inter San Fernando de Valle de Catamarca et Miraflores, 600 m, Catamarca (Argentina)

• Gymnocalycium stellatum subs. occultum Frič ex H.Till & W.Till
• Gymnocalycium occultum (Frič ex H.Till & W.Till) H.Till

• Gymnocalycium stellatum (Speg.) Speg.
• Echinocactus stellatus Speg.
• Gymnocalycium asterium A.Cast.
• Gymnocalycium quehlianum var. stellatum (Speg.) Dölz
• Gymnocalycium stellatum var. paucispinum (Backeb.) R.Strong
• Gymnocalycium asterium var. paucispinum Backeb.

• Gymnocalycium stellatum subs. occultum Frič ex H.Till & W.Till
• Gymnocalycium occultum (Frič ex H.Till & W.Till) H.Till

Description: Gymnocalycium occultumSN|14405]]SN|11501]] is a beautiful, slowly-growing plant with a noticeably flatten body, at first solitary, later clustering.
Taxonomic note: What is Gymnocalycium occultumSN|11501]]SN|11501]]? Even the arch-splitter Backeberg abandoned G. occultum with the revealing comment that it was probably Gymnocalycium bodenbenderianumSN|11501]]SN|14405]].
Stem: Dark grayish-brown to olive-coloured epidermis, flattened globose, 7.5-10 cm in diameter. It will offset after a considerable period of time.
Ribs: 7-11, flat, round, without prominent chin-like protrusions.
Spines: 3-5, dark brown, becoming grey with age, spider-like, add-pressed, short, straight to slightly curved and flattened against the stem (rarely sticking out - easy cactus to handle).
Flowers: Creamy-white with a dull red throat, up to 6,5 cm. long, 4.5 cm. in diameter.
Fruits: Cylindrical.
Blooming season: Flowers are produced in late spring and remain open for up to twelve days.

Bibliography: Major references and further lectures
1) Edward Anderson “The Cactus family” Timber Press, Incorporated, 2001
2) David R Hunt; Nigel P Taylor; Graham Charles; International Cactaceae Systematics Group. "The New Cactus Lexicon" dh books, 2006
3) Roberto Kiesling, Omar E. Ferrari “Cien cactus argentinos” Editorial Albatros, 2005
4) N. L. Britton, J. N. Rose “The Cactaceae. Descriptions and Illustrations of Plants of the Cactus Family.” Volume 4, The Carnegie Institution of Washington, Washington 1923
5) Curt Backeberg “Die Cactaceae: Handbuch der Kakteenkunde” Gustav Fischer Verlag, Stuttgart New York 1982–1985
6) James Cullen, Sabina G. Knees, H. Suzanne Cubey "The European Garden Flora Flowering Plants: A Manual for the Identification of Plants Cultivated in Europe, Both Out-of-Doors and Under Glass" Cambridge University Press, 11/Aug/2011.
7) Cactus and Succulent Society of Great Britain “Cactus and Succulent Journal of Great Britain”, Volumes 39-43 page 79, 1977.

Cultivation and Propagation: Gymnocalycium stellatumSN|11493]]SN|11493]] is supposed to be one of the most difficult species in cultivation, and very slow to get to a reasonable size. It will offset after a considerable period of time.
Soils: It likes very porous standard cactus mix soil. Prefer a low pH compost, avoid substrata rich in limestone; otherwise growth will stop altogether.
Repotting: This plant needs plenty of space for its roots, repotting should be done every other year or when the it has outgrown its pot. Use pot with good drainage.
Watering: It is a summer-growing species that needs regular water in summer, but do not overwater (Rot prone), keep dry in winter at a minimum temperature of 0°C.
Fertilization: Feed with a high potassium fertilizer in summer.
Hardiness: Reputedly resistant to frost if kept on the dry side prior to, and during, cold weather (hardy to -12 C ° C, or less for short periods).
Exposition: The plant tolerates extremely bright situations but enjoys filtered sunlight or afternoon shade, inside it needs bright light, and some direct sun. Tends to bronze in strong light, which encourages flowering and heavy spine production, but is likely to suffer from sun scorch or stunted growth if over exposed to direct sunlight during the hottest part of the day in summer.
Uses: It is an excellent plant for container growing. It always looks good and stays small. It look fine in a cold greenhouse and frame or outdoor in a rockery.
Pests & diseases: It may be attractive to a variety of insects, but plants in good condition should be nearly pest-free, particularly if they are grown in a mineral potting-mix, with good exposure and ventilation. Nonetheless, there are several pests to watch for:
- Red spiders: Red spiders may be effectively rubbed up by watering the plants from above.
- Mealy bugs: Mealy bugs occasionally develop aerial into the new growth among the wool with disfiguring results, but the worst types develop underground on the roots and are invisible except by their effects.
- Scales: Scales are rarely a problem.
- Rot: This species is particularly easy and accommodating, seldom suffer of cryptogamic diseases. Rot it is only a minor problem with gymnocalyciums if the plants are watered and “aired” correctly. If they are not, fungicides won't help all that much.
Propagation: Direct sow after last frost(seldom produces offsets). Seeds germinate in 7-14 days at 21-27° C in spring, remove gradually the glass cover as soon the plants will be well rooted (ca 1-2 weeks) and keep ventilated, no full sun for young plants!