Xerophyte

Habit

It makes a cluster of basal stems.

Central Spines

Absent or occasionally one in Mammillaraia alamensis and Mammillaraia pseudoalamensis ( 1 to 4 in M. sheldonii), if present elongated and either straight or hooked, about 9 mm long long, brownish, the upper part dark blackish brown.

Seeds

Black, round, finely dotted..Taxonomy notes. Mammillaria pseudoalamensis crops up in commercial listings now and again, but almost invariably turns out to be Mammillaria sheldoniiSN|8833]]SN|8816]], with a greater radial spines count then Craig called for it M. alamensis ( 9 ) and usually more than the one central described. Reppenhagean favours the name, bur without justifying it in any way. It also surfaced under a Lau collection number (LAU 1401) and it remains to be seen if once again we have a M. sheldonii. If the required spine-count were found in plants resulting from these collections, we would still have merely an extension to the range of variability of M. sheldonii or even Mammillaria mazatlanensisSN|8816]]SN|9256]].

Description

Mammillaria sheldoniiSN|9256]]SN|8816]] is undoubtedly a variable species, which has given rise to several names now ascribed to synonymy. Mammillaria alamensisSN|8816]]SN|8833]] is nothing else than a variant recognisable for the absence of central spines, fewer radial spines (as low as 9) and larger flowers with distinctive orange stigma lobes. The otherwise identical Mammillaria pseudoalamensis instead has green stigma lobes.

Tubercles

Cylindrical four-sided basally, carinate, without latex, axils without wool but with an occasional few bristles. Tubercle arrangement 8-13.

Flowers

Large up to 3,5, wide funnel-form, diurnal, inodorous, light purplish-pink with a pinkish brown midstripe and paler margins. Stigmas are green (dull orange in M. pseudoalamensis)

Blooming Season

Spring, and flowers remain open for about three or four days.

Stem

Spherical to slender-cylindrical, dull green, often becoming reddish, 3-4 cm wide, 4-8 cm tall (or more in cultivation)

Radial Spines

M. alamensis usually has fewer radial spines than Mammillaria sheldoniiSN|8816]]SN|8816]] (as low as 9), white, tipped brown, needle-like, about 6 mm long.

Fruits

Berry-like, club shaped, pale scarlet about 20-25 mm long.