Origin and Habitat: Gymnocalycium ragoneseiSN|11496]]SN|21425]] has a very restricted range in Catamarca (and Cordoba?), Argentina (extent of occurrence is less than 100 km2).
Altitude: It grows at low elevation of 100 to 200(-400) metres above sea level.
Habitat and Ecology: Gymnocalycium ragonesi grows semi-buried at the edge of saline grasslands. The concentration of salts is high in the surface of the ground, but it decreases deeper down where the roots grow. The major threat for this species is illegal collection. It grows together with Gymnocalycium schickendantzii, Gymnocalycium asteriumSN|21425]]SN|11496]] v. paucispinum and Setiechinopsis mirabilisSN|3878]]SN|3878]].

• Gymnocalycium ragonesei A.Cast.

• Gymnocalycium ragonesei A.Cast.
• Gymnocalycium obductum Piltz
• Gymnocalycium stellatum var. obductum (Piltz) H.Till & W.Till
• Gymnocalycium ragonesei f. cristatum hort.
• Gymnocalycium ragonesei f. rubra hort.
• Gymnocalycium stellatum var. minimum (Pazout) R.Strong
• Gymnocalycium asterium var. minimum Pazout

Description: Gymnocacalycium ragonesei (Sometimes wrongly spelled “ragonesi” or “ragonesii”) is a very small, dark skinned cactus resembling a round brown rock with white flowers usually in clusters from June to September.
Habit: It is a slowly growing succulent species, usually solitary, but sometimes cespitose.
Stem: Very flattened globose, almost disk shaped, greenish grey, dark greyish-brown, dull olive-green, purplish brown to almost brick-red coloured, barely rising above ground level (1,4-2,5 cm tall) and up to 5(-7,5) cm in diameter.
Ribs: 7-10, very flat, separated by poorly delineated transverse furrows.
Spines: Short, 5-5, usually 6, thin, almost hairlike, pale creamy-white to greyish-white, with darker tips, to 3 mm long, spidery, flattened against stem (rarely sticking out - easy cactus to handle).
Flowers: 2-3 at any one time near centre of plant, funnel shaped with narrow floral tube, creamy-white with a dull red throat, up to 3-4(-5) cm long, 3-4(-4,5) cm diameter. Outer perianth segments greyish with white margins, inners ones white, often with light grey midstripe.
Blooming season: Flowers are produced in late spring and remain open for up to twelve days.
Fruits: Slender, ovoid or spindle shaped, greenish brown, to 2,5-4 cm long, grey with pale edged margins.
Seeds: Glossy chestnut-brown 1,5 by 1 mm broad.Hilum large, pale with spongy margins.

Bibliography: Major references and further lectures
1) Trevisson, M., Demaio, P. & Perea, M. 2013. Gymnocalycium ragonesei. In: IUCN 2013. "IUCN Red List of Threatened Species." Version 2013.2. <www.iucnredlist.org>. Downloaded on 31 December 2013.
2) Edward Anderson “The Cactus family” Timber Press, Incorporated, 2001
3) David R Hunt; Nigel P Taylor; Graham Charles; International Cactaceae Systematics Group. "The New Cactus Lexicon" dh books, 2006
4) Roberto Kiesling, Omar E. Ferrari “Cien cactus argentinos” Editorial Albatros, 2005
5) 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
6) Hans Krainz “Die Kakteen: eine Gesamtdarstellung der eingeführten Arten nebst Anzucht- und Pflege-Anweisung” Franckh'sche Verlagshandlung” Lfg. 59. 1974

Cultivation and Propagation: Gymnocalycium ragoneseiSN|21425]]SN|21425]] 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 if not at all.
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 over-water ). Keep rather 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 -5 C ° C, or less for short periods).
Exposition: The plant tolerates 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!