Mammillaria grusonii

Mammillaria grusonii SB1725 Viesca, Coahuila, Mexico
 

Description: It is undoubtedly one of the largest species in the genus and usually solitary (it has a tendency to remain the same in the culture).  It reveals its true beauty only as it becomes 6 -10 years old, and reaches 30 cm or more in diameter.
Stems: globose to thick cylindrical, light blue-green, up to 30 cm and 25 cm in diameter.
Tubercles: Basally four-angled , carinate, without latex, the axil is woolly at first, later naked.
Radial spines: 12 - 14, straight, needle-like, upper ones shorter, 6 - 8 mm long, at first reddish,  tipped brown, later grey or snowy- white.
Central spines: Usually 2 (or rarely 3), straight, stronger than the radial, one ascending, one descending, 4 - 6 mm long.
Flowers: Bell shaped, funnel-form, diurnal, light yellow-cream or pinkish with darker (brown or purple) midstripe with a yellowish throat, up to 25 mm long and in diameter.
Blooming season: Spring, and flowers remain open for about three or four days.
Fruits: Scarlet, club shaped
Seeds: Brown.

Recognized subspecies, varieties and forms:

Mammillaria pachycylindrica (Reppennhagen considered it a separate form) with more spines, 20–23 grayish-white radials and about 6 centrals, at first dark, blackish-brown, becoming gray, tepals lobes with a wide brownish-pink midstrip.
Mammillaria durangicola  This form has 10-16 radials, 4-15 mm long, 1 - 3 central, 10-17mm long, black, and flowers as in Mammillaria pachycylindrica, with a brownish midstrip.
Mammillaria papasquiarensis is a longer form, with 8-10 radial spines, 5-40 mm long, and 1 to 3 central spines, 40 - 100 mm long.  The flowers are white with a pinkish midstrip.
Mammillaria zeyeriana :  The spines are of  intermediate measurement, of which the radials are 10 to 15,  8-15 mm long, and the centrals usually 4 (but sometime up to 6), 12 - 25 mm long.   The flowers are similar to the last  mentioned.
Mammillaria mexicensis  has  dark pink flowers.
 

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Scientific name:  Mammillaria grusonii
First description:  by Runge, Gartenflora 38: 105 with fig. (1889)

Origin:  Mexico, COAHUILA (Sierra Bola, Cerro Bola, Viesca, Puerto de Ventanillas, San Pedro de las Colonias, Cuatrocienegas, Cerro Zavaleta, El Carmen, San Rafael, Pinaje de Leone, Pomona/Paile, La Pena, Tacubaya, Torreon - Cuencame, San Antonio, El Amparo, La Cuchilla), and DURANGO (Penon Blanco, Nazas - Rodeo, Belem, La Concha, Cuencame, San Bartolo, Cerro Visnaga, Lerdo, Santiago Papasquiaro)

Habitat: Grows on the top and slope of hills, or in flat areas at about 800 - 1.850 m of altitude

Conservation status:  Listed in CITES appendix 2.

Synonyms:  

• Mammillaria mexicensis R.T.Craig
• Mammillaria pachycylindrica  Backeb.
• Mammillaria zeyeriana K.Schum
• Mammillaria durangicola
• Mammillaria papasquiarensis
• Mammillaria tesopacensis var. papasquiarensis

Cultivation: This plant blooms easily and needs lots of light.  Use a pot with good drainage and a very porous mineral-based potting mix.  Potted plants are quite wet-sensitive, especially in light of its small root system. Water sparingly during the growing season, let soil dry in between to prevent root rot, keep very dry in winter.  Feed with a high potassium fertilizer  in summer.
Usually it is recommended to over-winter this plant in a bright and warm greenhouse with at least 8-10° C , but it has proven to be quite frost resistant (if kept dry it is hardy as low as -7° C).  A resting period in winter and strong light are necessary so that it can flower properly.   Plants will offset readily, and dense clumps can be produced in a very few years.

Propagation: Through seeds and cuttings.

Photo of conspecific taxa, varieties, forms and cultivars of  Mammillaria grusonii

• Mammillaria grusonii