Origin and Habitat: Mexico, (at the border of the states of Puebla and Oaxaca).
Habitat: Altitude 800 to 1.000 m.

• Mammillaria crucigera subs. tlalocii f. caespitosa hort.
• Mammillaria tlalocii f. caespitosa hort.

• Mammillaria crucigera Mart.
• Cactus cruciger (Mart.) Kuntze
• Cactus curvispinus (Otto) Kuntze
• Mammillaria curvispina Otto
• Mammillaria discolor var. curvispina (Otto) Salm-Dyck
• Mammillaria crucigera var. grandinosa Lizen et al.

• Mammillaria crucigera subs. tlalocii (Repp.) D.R.Hunt
• Mammillaria crucigera var. tlalocii (Repp.) Lizen et al.
• Mammillaria tlalocii Repp.
• Mammillaria buchenaui Backeb.
• Mammillaria crucigera subs. tlalocii f. caespitosa hort.
• Mammillaria tlalocii f. caespitosa hort.
• Mammillaria crucigera subs. tlalocii f. cristata hort.
• Mammillaria tlalocii f. cristata hort.

Description: Globular cactus, solitary or clumping dichotomously; usually this species don't produces lateral shoots. But in cultivation are frequently seen plant that branch profusely from the base.
Stem: Globose, later columnar, curving pipe-shaped, to 20 cm long, 5 to 7 cm wide. The axil is white-wooled.
Radial spines: 16 to 22, glassy white, 1 to 2 mm long, the longer sideways pointing.
Central spines: On the areoles at the apex of the plant, with age, may appear a single longer brown-black central spine 6-10 mm long.
Flowers: Carmine-pink, 12 to 14 mm long, 8 to 10 mm wide.
Flowering time: Blooms in late winter, early spring.
Fruits: Carmine-pink small.
Seeds: Small, brown.

Notes: This is one of the Mammillaria commonly called "Owl Eye Cactus", known for dichotomous branching (forking or dividing into two parts). Although dichotomous branching is not a common occurrence in cacti in general, it happens for some reason in this particular subspecies. What is interesting about this cactus is that it began as a single head, and it has now divided twice, forming what will be four separate branches. When the division process started, it was obvious that four heads would appear, but I don’t think the one head divided quadruply. Most probably, one head became two, and then those two immediately divided.
Other Owl Eye Cactus among others comprise Mammillaria karwnskiana, Mammillaria formosaSN|15832]]SN|15832]], Mammillaria microthele and Mammillaria perbella.

Bibliography: Major references and further lectures.
1) Robert T. Craig “The Mammillaria handbook: with descriptions, illustrations, and key to the species of the genus Mammillaria of the Cactaceae” E P Publishing, 1945
2) John Pilbeam “Mammillaria The Cactus File Handbook” Cirio Pub. Services, 01/Dec/1999
3) Edward Anderson “The Cactus family” Timber Press, Incorporated, 2001
4) 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
5) David R Hunt; Nigel P Taylor; Graham Charles; International Cactaceae Systematics Group. "The New Cactus Lexicon" dh books, 2006

Cultivation and Propagation: It is a slow growing species . Use pot with good drainage and a very porous mineral-based potting mix, keep dry in winter. Pot plants are quite wet-sensitively. Care must be taken with watering (Rot prone) and needs good drainage. Water sparingly during the growing season, keep very dry in winter. Feed with a high potassium fertilizer in summer.
Usually it is recommended to overwinter this plant in a bright and warm greenhouse with at least 8-10° C , but it proved to be quite frost resistant (if kept dry it hardy as low as -5° C)Outside full sun or afternoon shade, inside needs bright light, and some direct sun.
Some plants will offset readily, and clumps can be produced in a very few years.
Propagation: Direct sow after last frost, cuttings or grafting.