Scientific: Mammillaria hahniana (formerly Mammillaria microcarpa)
Common: old lady cactus, birthday cake cactus
Family: Cactaceae
Origin: Slopes and canyons of submontane matorral and deciduous forest in the central Mexico regions of Guanajuato, Hildago, Queretaro, and San Luis Potosí.

Pronounciation: Mam-a-LAR-ee-a hahn-ee-AY-na

Hardiness zones
Sunset
11-13
USDA 9 (with protection)-11

Landscape Use: This is an excellent small for intimate scale desert, rock and succulent gardens, containers. In temperate climates this is a collectors cactus that is grown under environmentally-controlled conditions such as a glass- or greenhouse.

Form & Character: Rounded to cylindrical, diminuative, dainty, pure.

Growth Habit: Mostly a diminuative branched barrel cactus to 8 inches tall that grows during the warm season and is generally quiescent during winter.

Foliage/Texture: Short white spines with occassional red tips, 20 to 30 per areole in several series but all equally thin, stems globular when young, more cylindrical with age, much branhed with age; medium texture.

Flowers & Fruits: Produces a ring of small and delicate pink magenta star-shaped flowers with protruding yellow anthers; fruits small, globular, orange, rare in Phoenix.

Seasonal Color: Flowers profusely during winter to early spring.

Temperature: Tolerant

Light: Full sun to partial shade. Needs protection from landscape western sun in Phoenix (especially strong reflected western light), however, it grows best in an eastern exposure.

Soil: Must have a well-drained, sandy to gravely soil.

Watering: Rarely needs supplemental irigation, especially during winter.

Pruning: None

Propagation: Seed, tissue culture.

Disease and pests: Root rot in poorly drained and overwatered soil.

Additional comments: Great small barrel cactus for textural and color accent in small scale landscape settings. The cultivar 'Superba' has a dense array of elongated trichomes around the barrel terminus giving it a white "hairy wig" appearance. Old lady cactus is deemed as near threatened (population decreasing) in its native range.