Origin and Habitat: Buenos Aires, Argentina.
Altitude: It grows at low elevation around 50 metres above sea level.

• Gymnocalycium gibbosum var. nigrum Backeb.

• 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 gibbosum var. nigrumSN|8057]]SN|13944]] a.k.a. “Black Chin Cactus ” is one of the controversial forms of the very variable Gymnocalycium gibbosumSN|8057]]SN|8057]]. The variety “nigrum” has jet- black spines on a nearly black body and large off-white flowers about 6 cm tall. However it look very similar to other varieties of Gymnocalycium gibbosumSN|13944]]SN|8057]] which are linked one to each others by populations of plants with intermediate characteristics. Nowadays all them are thought to belong to a unique polymorphic species. Such variations has led to establishment of several unnecessary names for this species.
Habit: It is a small solitary cactus.
Stem: Deep glaucous-green, dark olive green to grey-black, discoidal that became elongate with time 10-25 cm tall, up to 12 cm in diameter, the apex is slightly woolly. This stem tends to become rather greener with age especially if grown somewhat shaded.
Ribs: 10-16 straight, divided in well distinct angular ribs.
Areoles: Greyish, elongate.
Radial spines: 5 to 7 or more, less 20-25 mm long mm long slightly bent against the plants body, fairly stout, blackish, becoming 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(-80) 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.

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” Volume V, Gustav Fischer Verlag, Stuttgart New York 1982–1985,
6) Walther Haage “Cacti as House Plants” Studio Vista, 1965
7) Margaret J. Martin, Peter Richard Chapman, Hugh Ambrose Auger “Cacti and their cultivation." Scribner's, 1975

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: Division, 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! To make a cutting twist off a branch and permit it to dry out a couple of weeks, lay it on the soil and insert the stem end partially into the soil. Try to keep the cutting somewhat upright so that the roots are able to grow downward.