Mammillaria pseudoalamensis (= M. alamensis)
(Syn: Mammillaria sheldonii)

Mammillaria pseudoalamensis (= M. alamensis)
Now often considered a synonym of  Mammillaria sheldonii, to which it shows only modest differences: absence of central spines and  larger flowers with a characteristic distinctive orange pistil.
 

Photo of conspecific taxa, varieties, forms and cultivars of plants belonging to the Mammillaria sheldonii complex (This Taxon has lots of synonyms ( like many other cacti), with several controversial varieties and subspecies, and comprises a multitude of different forms, but where each form is linked to others by populations of plants with intermediate characteristics):

• Mammillaria swinglei (M. sheldonii)
• Mammillaria pseudoalamensis (M. sheldonii)

Mammillaria pseudoalamensis Backeb.

Scientific name:  Mammillaria sheldonii (Britton & Rose) Boed.

First description: by Britton & Rose, The Cact. 4: 156 (1923).
 
Origin:  Sonora, and Chihuahua

Conservation status:  Listed in CITES appendix 2.

Synonyms:

• Mammillaria alamensis R.T.Craig

Description: Mammillaria sheldonii is undoubtedly a variable species, which has given rise to several names now ascribed to synonymy.
The M. pseudoalamensis (= M. alamensis) is nothing else than a variant recognisable for the absence of central spines, and larger flowers with a characteristic distinctive orange pistil.
Habit:  It makes a cluster of basal stems.
Stem: spherical to slender-cylindrical, dull green, often becoming reddish, 3-6 cm wide, 8-15 cm tall (or more in cultivation)
Tubercles: Cylindrical four-sided basally, carinate, without latex, axils without wool but with an occasional few bristles. Tubercule arrangement: 8 - 13
Radial spines: The number of radial spines varies from as low as 9 (M. alamensis) to as many as 24, white, tipped brown, needle-like, about 6 to 8 mm long.
Central spines: 1 to 4 ( 0 in M. alamensis), the lower une elongated and either straight or hooked, 1 to 15.cm long, brownish, the upper part dark blackish brown.
Flowers: Large, wide funnel-form, diurnal, inodorous, light purplish-pink with a pinkish brown midstripe and paler margins, about 20 cm in diameter (up to 3,5 in M. alamensis). Stigmas are green (Orange in M. alamensis)
Blooming season (Europe): Spring, and flowers remain open for about three or four days.
Fruit: Club shaped, pale scarlet 25-30 mm long.
Seed: black.
 

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.