Origin and Habitat: Argentina Catamarca ( Angostura de Guanchim and Tinogasta ) and Bolivia border.
Altitude: (1300?)2200-2900 metres above sea level.
Habitat It grows fully exposed to blazing hot sun in an extremely arid habitat, between red violet coloured rocks and gravel in flat or moderately step and very drained clayey and sandy soils. It it is often found growing along with a very sparse vegetation of Puna bonnieaeSN|1023]]SN|1023]], Lobivia famatimensisSN|3315]]SN|3315]] v. bonnieae, Echinopsis leucanthaSN|8246]]SN|8246]], Pterocactus tuberosusSN|1126]]SN|1126]], Cumulopuntia sp., Maihueniopsis sp. and Opuntia sulphurea.

• Tephrocactus geometricus f. inermis hort.

• Tephrocactus geometricus (A.Cast.) Backeb.
• Opuntia geometrica A.Cast.
• Tephrocactus alexanderi var. geometricus (A.Cast.)
• Tephrocactus geometricus f. inermis hort.

Description: Tephrocactus geometricusSN|14349]]SN|14349]] is an extraordinary species that shows a strong adaptation to extreme desert habitat, with dwarf growth and geophytic habit. The "inermis" (Spineless form) is only an extremely short spined form, but both short and long spined plants (with all intermediate spine length) are found throughout the distribution range of the species and it difficult to classify Tephrocactus geometricusSN|14349]]SN|14349]] f. inermis as a separate variety. It is one of the showiest “opuntia” species sought-after by cacti impassioned a strange "geometric" plants but fabulous flowers.
Habit: Small low-growing globular segmented cactus loosely branched into small clumps.
Stem segments: 4-5 cm in diameter, clear glaucous/blue that reddens to purple in full sun exposure. New growing cladodes are dark purple.
Leaves: Very reduced, ephemeral.
Areoles: A caducuous white felt is present in young areoles.
Glochids: Not present, or very reduced.
Spines: Spineless, or with very short thin spines sporadically present in the upper areoles, 2-3mm long, appressed and turned downward.
Flower: White to light pink with a darker midstrip. Flowers last only one day.

Notes: Tephrocactus geometricusSN|14349]]SN|14349]] is an example of hexagonal configurations of stem-segments surface, other plant that show hexagonal tubercles comprises Matucana krahniiSN|6031]]SN|6031]] and Thelocactus hexaedrophorusSN|10830]]SN|10830]].

Bibliography: Major references and further lectures
1) Curt Backeberg “Die Cactaceae: Handbuch der Kakteenkunde” Volume 1G. Fischer, 1958
2) Stuart Max Walters “The European garden flora. 3.[Angiospermae], Dicotyledons. [Casuarinaceae to Aristolochiaceae]” Cambridge University Press, 1989
3) Edward Anderson “The Cactus family” Timber Press, Incorporated, 2001
4) W. Stuppy “A new combination in Tephrocactus Lem. (Cactaceae)” Kew Bulletin 56:1003-1005 2001
5) 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
6) David R Hunt; Nigel P Taylor; Graham Charles; International Cactaceae Systematics Group. "The New Cactus Lexicon" dh books, 2006
8) Clive Innes, Charles Glass “The Illustrated Encyclopedia of Cacti” Knickerbocker Press, 1997

Cultivation and Propagation: It is susceptible to overwatering, but need enough water during the growing season. This mountain cactus - because of the elongated fat taproot - necessitate deep pots and a well drained mineral potting mix. It prefers a full sun exposure, but should be protected from excessive heat and sun in summer.
Frost Tolerance: They tolerate light frost -5 (-10) °C.
Need to be kept in a cool place during winter rest this is important for the flowers as well as for their health. Without this cool winter period they normally wont get many buds. Keep dry in winter to avoid rot. Need a sufficient amount of air.
Propagation: Seeds are extremely difficult to germinate. Best reproduced from rooted cuttings. Grafting is often used to speed growth rate and to create a back-up for plants in collection.