Origin and Habitat: Catamarca, Córdoba, La Rioja, Argentina.

• Gymnocalycium triacanthum Backeb.

• Gymnocalycium bodenbenderianum (Hosseus ex A.Berger) A.W.Hill
• Echinocactus bodenbenderianus Hosseus ex A.Berger
• Gymnocalycium pseudoragonesei Schuetz
• Gymnocalycium riojense Frič ex H.Till & W.Till
• Gymnocalycium riojense subs. guasayanense (Strigl) H.Till
• Gymnocalycium riojense var. guasayanense Strigl
• Gymnocalycium riojense var. guthianum H.Till & W.Till
• Gymnocalycium riojense var. mirandaense H.Till & W.Till
• Gymnocalycium riojense subs. paucispinum Backeb. ex H.Till & W.Till
• Gymnocalycium paucispinum (Backeb. ex H.Till & W.Till) H.Till
• Gymnocalycium riojense subs. piltziorum Schütz ex H.Till & W.Till
• Gymnocalycium riojense var. pipanacoense H.Till & W.Till
• Gymnocalycium riojense var. platygonum Schütz ex H.Till & W.Till
• Gymnocalycium platygonum (H.Till & W.Till) Pilbeam
• Gymnocalycium riojense var. sanjuanense H.Till & W.Till
• Gymnocalycium riojense var. vertongenii Amerh.
• Gymnocalycium triacanthum Backeb.

• Gymnocalycium bodenbenderianum subs. intertextum (Backeb. ex H.Till) H.Till
• Gymnocalycium intertextum Backeb. ex H.Till
• Gymnocalycium bodenbenderianum subs. intertextum var. moserianum Schuetz ex H.Till
• Gymnocalycium intertextum var. moserianum H.Till
• Gymnocalycium moserianum Schütz
• Gymnocalycium knollii Mereg.
• Gymnocalycium kozelskyanum Schütz
• Gymnocalycium riojense subs. kozelskyanum Schuetz ex H.Till & W.Till

Description: Gymnocalycium triacanthumSN|14405]]SN|21403]] is a small single headed, flattened cactus, with peculiar grey bodies with short adpressed spines in clusters of three. It is one of the several species of the variable Gymnocalycium bodenbenderianumSN|21403]]SN|14405]] complex, however it is hard to tell it apart from the three spined "bodenbenderianum", and most authors choose to lump them together.
Habit: It is a geophyte stem succulent plant usually solitary and barely rising above ground level with a swollen underground root system.
Stem: Flat, disc-shaped, 2-3 cm tall and up to 8 cm in diameter, grey-green to dull brownish-green.
Ribs: 11-15 low, rounded and slightly tuberculate, with tubercles separated by furrows.
Central spines: Absent.
Radial spines: usually 3, occasionally up to 5 or more, up to 10 millimetres long, sharp, stout, but not harmful, backward curved, blackish brown, becoming grey with age.
Flowers: Near the apex, white to pale pink, 3,5 to 6 cm long. Flower tube narrow with green scales tinged brown; outer tepals pale brownish-green; inner perianth-segments linear-lanceolate, white or pinkish. Throat reddish.
Flowering time: Blooms appear recurrently from June to autumn. It flowers quite readily as a young seedling.
Fruits: Blue-green, ovoid, up to 2 cm long (or longer) and up to 1 cm in diameter.

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)Curt Backeberg “Die Cactaceae: Handbuch der Kakteenkunde” Gustav Fischer Verlag, Stuttgart New York 1982–1985

Cultivation and Propagation: Gymnocalycium triacanthumSN|21403]]SN|21403]] is a summer grower species that is easy to cultivate.
Growth rate: It is a relatively slow growing and easily flowering species that will make clumps given the best conditions.
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: Needs moderate to copious waterings 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 -5 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. In full sun turns an uneven brownish red colour.
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. 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!