Origin and Habitat: Uruguay, East Paraguay, South Brasil and Northeast Argentina.(extent of occurrence is 40,000 km2)
Altitude: It grows at elevations up to 300 m asl.
Habitat and Ecology: Gymnocalycium horstiiSN|18875]]SN|18875]] grows on rocky outcrops in pampa grasslands. It has a relatively wide range, but the species is scarce and the population severely fragmented. The area where it occurs is under several pressures, such as cattle grazing, agriculture, fire and illegal collection.

• Gymnocalycium horstii Buining

• Gymnocalycium horstii Buining
• Gymnocalycium horstii subs. megalanthum Amerh.

• Gymnocalycium horstii subs. buenekeri (Swales) P.J.Braun & Hofacker
• Gymnocalycium buenekeri Swales
• Gymnocalycium horstii var. buenekeri (Buining)

Description: Gymnocalycium horstiiSN|18878]]SN|18875]] is a distinctive large cactus, minimally spined with a green ball-shaped body. Usually solitary or slowly clustering as they age. Two subspecies are recognized, the nominate form and subsp. buenekeri (Swales) P.J.Braun & Hofacker. The latter was previously considered a good species, genetic studies are required to see if it should be raised to species level again.
Stem: Smooth, globoid, shiny green, up to 20(-25) cm in diameter.
Ribs: 5-6 cm wide, rounded, somewhat acute, deeply furrowed.
Spines: Few (usually 5 of which one pointing downward others to the sides) , yellowish white, sparse, straight to slightly curved, definite and very irregular, up to 3 cm long.
Flowers: White, pale pink, pink or pale purplish up to 11 cm long and in diameter.
Fruits: Ovoid, blue-green.
Remarks: Gymnocalycium buenekeriSN|18875]]SN|18878]] and G. horstii are very similar if not identical, both have very similar great pink flowers and the same (usually) five ribbed appearance, and good yellow spines.

Bibliography: Major references and further lectures
1) Edward Anderson “The Cactus family” Timber Press, Incorporated, 2001
2) 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
3) David R Hunt; Nigel P Taylor; Graham Charles; International Cactaceae Systematics Group. "The New Cactus Lexicon" dh books, 2006
4) Larocca, J. & Machado, M. 2013. Gymnocalycium horstii. In: IUCN 2013. "IUCN Red List of Threatened Species." Version 2013.2. <www.iucnredlist.org>. Downloaded on 17 February 2014.

Cultivation and Propagation: Very easy to grow, this plants offers no cultivation difficulties. Summer grower needs moderate to copious waterings in summer (It enjoy more water than the average cactus). Quite frost resistant if kept dry in winter -4° C. Feed with a high potassium fertilizer in summer. Sun Exposure: Light shade. (Keep out of hot, direct sun or will burn badly but hot, blazing afternoon sun taking it well, just bronzing a bit)
Propagation: Seeds (seldom produces offsets)