Mammillaria Crucigera

Mammillaria crucigera SB529 Teotitlan del Camino, Oaxaca, Mexico, 500m.
The typical form of this intriguing species is known from a very long time, but it is still very rare  in collections, the slow growth rate make it one of the most sought-after and highly priced of all  mammillarias.
 

Description: Globular very slow growing cactus with small spines, solitary or clumping almost always forking dichotomously at maturity.
Stems: Heads flattened globose to short cylindrical, curving pipe-shaped,, up to 10 cm tall and 4 - 6 cm in diameter, ranging from olive green to grey-green to almost brown to almost purple.
Tubercles: Closely set, firm, not sharply angled, keeled with their axils full of white wool, Some latex is present in the growing season.
Areoles: Reddish-brown.
Radial spines: 22 - 30, finely needle-like or bristly, glassy white, to 2 mm long.
Central spines: 4 (-5), yellowish or brown, rigid, to 2 mm long.
Flowers: Small , funnelform,up to 1.2 cm, deep pink, rarely rising above the spines.
Blooming season: Flowers in late winter, early spring.
Fruits: Pink to red.
Seeds: Small, brown.

Recognized subspecies, varieties and forms:

M. crucigera ssp crucigera divides dichotomously and also offsets lower on the plant body.
M. crucigera ssp tlalocii forms simple columns (usually) without dividing or offsetting.
 

The short minute spines along with the tendency to branch dichtocomuously  (each head splitting into
into 2 or more heads) make this one of showiest and prettiest species of Mammillaria.

Scientific name:  Mammillaria crucigera
First description by Martius, Nova Acta Acad. Caes. Leop. Carol. German Nat. Cur. 16: 340, t. 27 (1832)

Origin:  Endemic to a small region in Central Mexico (at the border of the states of Puebla and Oaxaca)

Habitat: Grows on cliff edges clinging in clefts and crevasses in the rock often in mostly pure gypsum. Altitude 800 to 950 m.

Conservation status: Listed in CITES appendix 2.

Synonyms:

• Cactus crucigerus (Mart.) Kuntze
  in: Rev.Gen. Pl. 1:260. 18911891
• Mammillaria discolor var. curvispina
• Mammillaria crucigera var. grandinosa Linzen, Rogoz & Frank Wolf 1998
• Mammillaria crucigera subsp. tlalocii (Reppenhagen) D. R. Hunt 1997
• Mammillaria crucigera var. tlalocii (Repp.) Linzen, Rogoz & Frank Wolf 1998
• Mammillaria tlalocii Reppenhagen 1989
  Published in: Gattung Mammillaria 1988: 120 (1989)
• Mammillaria curvispina
• Cactus curvispinus
• Mammillaria buchenaui Backeberg ex Mottram 1980
• Mammillaria falsicrucigera Backeberg 1962

Cultivation: It is an extremely slow growing  species (hence the rarity and high prices in the trade).  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.

Photo of conspecific taxa, varieties, forms and cultivars of Mammillaria crucigera complex (This Taxon has lots of synonyms whit several controversial varieties and subspecies):

• Mammillaria crucigera
• Mammillaria tlalocii
• Mammillaria tlalocii "caespitosa"