Origin and Habitat: Nursery selected form (Japan)

• Gymnocalycium cardenasianum cv. Japanese Selection

• Gymnocalycium spegazzinii Britton & Rose
• Echinocactus loricatus Speg.
• Gymnocalycium loricatum Speg.
• Gymnocalycium spegazzinii subs. armatum (F.Ritter) Halda & Šorma
• Gymnocalycium armatum F.Ritter
• Gymnocalycium cardenasianum f. armatum (F.Ritter) H.Till & Amerh.
• Gymnocalycium spegazzinii var. armatum (F.Ritter) Slaba & Šorma
• Gymnocalycium spegazzinii subs. fiambalense
• Gymnocalycium spegazzinii var. horizonthalonium Backeb.
• Gymnocalycium horizonthalonium Frič ex Kreuz.
• Gymnocalycium spegazzinii var. major Backeb.
• Gymnocalycium spegazzinii var. punillense H.Till & W.Till
• Gymnocalycium spegazzinii var. recii Milt
• Gymnocalycium spegazzinii subs. sarkae Halda & Milt
• Gymnocalycium spegazzinii var. unguispinum Slaba

• Gymnocalycium spegazzinii subs. cardenasianum (F.Ritter) R.Kiesling & D.Metzing
• Gymnocalycium cardenasianum F.Ritter

• Gymnocalycium cardenasianum cv. Japanese Selection

Description: This is a special form of Gymnocalycium cardenasianumSN|995]]SN|995]] furnished with incredibly strong dark spines. It has been selected in Japan.
Stem: Grey green, compact, globular up to 12 (-15) cm wide 10 cm tall with a slightly concave woolly apex. Will not (usually) offset.
Spines: Long, stout, eagle claw-shaped, typically-twisted, up to 4 cm long. Black turning dark grey as they ages.
Flowers: Open petaled, funnel-shaped, about 4(-7) cm in diameter, 3(-5) cm tall and pinkish in colour. They grow near the apex. The flowers of Gymnocalycium cardenasianumSN|995]]SN|995]] have a tough time trying to force themselves through the fierce spines, and is quite rare to see an open flower because the spines prevent the flowers from opening properly.
Blooming season: They will bloom at an early age and bloom sparingly in mid-summer.

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
6) John Borg “Cacti: a gardener's handbook for their identification and cultivation” Blandford P., 1970

Cultivation and Propagation: Gymnocalycium cardenasianumSN|995]]SN|995]] is a summer grower species that is easy to cultivate.
Growth rate: It is a slow growing and easily flowering species.
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.