Description: Mammillaria sheldonii
is undoubtedly a variable species, which has
given rise to several names now ascribed to synonymy. 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 one 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. pseudoalamensis)
Blooming season: Spring, and flowers
remain open for about three or four days.
Fruits: Club shaped, pale scarlet 25-30 mm long.