Origin and Habitat: Argentina, from north of Salinas Grandes, Catamarca, to East of Sierra Mazan, La Rioja.

• Gymnocalycium riojense var. platygonum Schütz ex H.Till & W.Till
• Gymnocalycium platygonum (H.Till & W.Till) Pilbeam

• 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 platygonumSN|21406]]SN|21411]] (firstly described as Gymnocalycium riojenseSN|11506]]SN|21407]] var. platygonum Schütz ex Till & W. Till in 1991) is a local or morphological form of the widespread and variable Gymnocalycium bodenbenderianumSN|21425]]SN|14405]]. It has a hemispherical, usually much depressed brownish-grey stem, with pearl-white scented flowers and 3 claw-shaped spines. However the distinguishing characteristics of Gymnocalycium platygonumSN|14405]]SN|21411]], appear to fall within the natural variation of Gymnocalycium bodenbenderianumSN|21411]]SN|14405]] and it should be synonymized with the latter, but it still has a value for a collector because they identify plants with particular characters. This taxon grows close to the habitats of Gymnocalycium ragoneseiSN|14405]]SN|21425]] and Gymnocalycium obductumSN|21407]]SN|11506]] and is closely related to Gymnocalycium riojense subs. paucispinumSN|21411]]SN|21406]].
Stem: Disc-shaped, flat, epidermis brownish-grey to brown-green.
Root: Turnip like, spherical, merging with the stem.
Ribs: 10 to 12, separated by a straight, longitudinal furrow, 23-24 mm wide, flat, more lifted towards the tip or the stem, with small chin-like protrusions.
Areole: Small, round, slightly nested, 3 x 3 mm, only the youngest with white felt, almost bare as they ages.
Spines: 3, claw-shaped, pointing downward, adpressed to the body, firm, brown when young, early greying, the two lateral 7-9 mm long, the intermediate one 3-5 mm long.
Flowers: From areoles near the top of fragrant, 45-48 mm long, 40-44 mm in diameter, pearly white with pink gloss, pink throat, sometimes brownish yellow. Outer tepals lanceolate, 22-24 mm long, 5-6 mm wide, pearly white with a pink belt and pink middle, sometimes greenish-brown at the base. Inner petals lanceolate, 18-21 mm long, 4 mm wide, pearly white, with pink, sometimes greenish-yellow base. Filaments greenish pink at the base, 6-8 mm long, arranged in two rows, the lowermost row close to the large pink nectarium (c.3.5 x 3.5 mm), the other inserted on the tube wall, anthers oval to oblong, yellow. Pistil about 17 mm long, 1.5 mm in diameter, stigma lobes mostly 7, yellow. Ovary with a heart-shaped chamber, 11-15 mm long, 5-7 mm wide.
Fruits: Oval to oblong-oval, 33-35 mm long and 10-11 mm in diameter, brownish-green, sometimes purple frosted, green seed loops.
Seed: With a wide concave horseshoe-shaped edge, that almost entirely covers the hilum area. Testa shiny, light brown, with small papillae.