Origin and Habitat: La Pampa and Río Negro Argentina
Type locality: Ruta 2, 30 km north of San Antonio de Oeste, Barrancas del Gualichos, Río Negro (Argentina)
Altitude: 50-400 metres above soil level.
Habitat: It grows among scrubs and stones in a semi-arid area characterized by an annual rainfall of 250 millimetres (mm) with significant fluctuations between years. During winter there are heavy snows and frosts can occur throughout the year; spring and autumn provide only short transitions between summer and winter. Although it does not rain much in the region on an annual basis, summers are usually mild, and the temperature sometimes gets very hot. The area does get very windy at times.

• Gymnocalycium gibbosum var. brachypetalum (Speg.) Papsch
• Echinocactus brachypetalus (Speg.) Werderm. in Backeb.
• Gymnocalycium brachypetalum Speg.

• Gymnocalycium gibbosum (Haw.) Pfeiff. ex Mittler
• Cactus gibbosus Haw.
• Cereus gibbosus (Haw.) Pfeiff.
• Echinocactus gibbosus (Haw.) DC.
• Gymnocalycium gibbosum var. brachypetalum (Speg.) Papsch
• Echinocactus brachypetalus (Speg.) Werderm. in Backeb.
• Gymnocalycium brachypetalum Speg.
• Gymnocalycium gibbosum f. cerebriformis (Speg.) Papsch
• Echinocactus gibbosus var. cerebriformis Speg.
• Gymnocalycium gibbosum var. chubutense (Speg.) Papsch
• Echinocactus gibbosus var. chubutensis
• Gymnocalycium chubutense (Speg.) Speg.
• Gymnocalycium gibbosum f. cristatum hort.
• Gymnocalycium gibbosum var. gerardii Boed.
• Gymnocalycium gerardii (Boed.) Y.Itô
• Gymnocalycium gibbosum var. leonense (Hildm. ex K.Schum.) Borg
• Echinocactus gibbosus var. leonensis Hildm. ex K.Schum.
• Echinocactus gibbosus f. leonensis (Hildm. ex K.Schum.) Schelle
• Gymnocalycium gibbosum var. leucacanthum (Rümpler) Borg
• Echinocactus gibbosus var. leucacanthus Rümpler
• Echinocactus gibbosus f. leucacanthus (Rümpler) Schelle
• Gymnocalycium gibbosum f. longispinum hort.
• Gymnocalycium gibbosum var. nigrum Backeb.
• Gymnocalycium gibbosum var. nobile (Haw.) Y.Itô
• Cactus nobilis Haw.
• Echinocactus gibbosus var. nobilis (Haw.) K.Schum.
• Echinocactus gibbosus f. nobilis (Haw.) Schelle
• Gymnocalycium gibbosum var. schlumbergeri (Rümpler) Borg
• Echinocactus gibbosus var. schlumbergeri Rümpler
• Echinocactus gibbosus f. schlumbergeri (Rümpler) Schelle

• Gymnocalycium gibbosum subs. borthii (Koop ex H.Till) G.J.Charles
• Gymnocalycium borthii Koop ex H.Till
• Gymnocalycium borthii subs. kokori Halda & Milt
• Gymnocalycium borthii subs. nogolense Neuhuber
• Gymnocalycium borthii var. viridis Neuhuber

• Gymnocalycium gibbosum subs. ferox (Labour. ex Rümpler) Papsch
• Echinocactus gibbosus var. ferox Labour. ex Rümpler
• Echinocactus gibbosus f. ferox (Labour. ex Rümpler) Schelle
• Gymnocalycium gibbosum var. ferox (Labour. ex Rümpler) Borg

Description: Gymnocalycium gibbosumSN|8057]]SN|8057]] var. brachypetalum is one of the several forms of the very variable Gymnocalycium gibbosumSN|8057]]SN|8057]] which form a complex of related taxon. It is still unclear whether this variable complex is one or several species. There is so much variation that most authors choose to lump them together. The variety "brachypetalum" distingushes for the unusual dark grey-green to nearly black stem and for the large white flowers.
Gymnocactus gibbosum is a low growing solitary cactus widely distributed in the mountains of Argentina from the south of the Buenos Aires province to Patagonia and show a great variability in morphological traits.
Stem: Deep glaucous-green to grey-black, discoidal that became elonged with time 10-25 cm tall, up to 12 cm in diameter, the apex is slightly woolly.
Ribs: 10-16 straight, divided in well distinct angular ribs.
Areoles: Whitish-grey, elonged.
Radial spines: 5-7 20-35 mm long slightly bent against the plants body, clear brown with a darker base when young, that became whitish-grey with a black base as they age.
Central spines: 0-2 very similar to the radials.
Flowers: Infundibuliform in the nearest periphery just around the apex 45-60 mm long, 60-65 in diameter. Tepals ivory white with a brownish mid rib or occasionally reddish, throat greenish with a basal reddish area. Style white-greenish, stigma white. Anthers cream coloured.
Fruits: Globate or fusiform, 20-40 mm long green with white bordered scales.
Remarks: It seems to be a pretty variable plant you might get some other names which are effectively the same plant.... and also not sure all plants identified as this are really this.

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) 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

Cultivation and Propagation: Gymnocalycium gibbosumSN|8057]]SN|8057]] is a summer grower species that is easy to cultivate.
Growth rate: It is a relatively rapidly 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 -12 C ° C, or less for short periods), but for safe cultivation it is best to avoid freezing temperatures.
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: Seeds (It don't 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!
Seed Collecting: Permit fruit to ripen, fruit must be significantly overripe before harvesting seed; clean and dry seeds.