Xerophyte

Habit

Solitary or with several stems from the base, sometimes branching.
Spheric to long-cylindrical, 4-25 (or occasionally up to 33 cm tall), 3-7 cm in diameter, blue-green, rounded apically, but there is no apical mat of pubescence.

Central Spines

1-4 per areole (sometimes absent), brown to brownish black, needle-like, , stout, 8-15 cm long, the lower one stouter and hooked, upper ones straight, ascending, like the radials,

Seeds

black, shining, minutely pitted.

Description

Mammillaria dioicaSN|916]]SN|916]] is a very spiny cactus often with flowers either all bisexual or all pistillate, a trait unusual for Cactaceae representatives.

Axils

Woolly and with 4-15 more or less setose bristles aslong as the tubercles.

Note

The dense covering of spines reduces the interception of solar radiation by the stem surface lowering the risks of overheating the apex during a summer day and of freezing during a winter night.

Tubercles

Firm, short cylindrical, without latex.

Flowers

Funnelform yellow to almost white with a pink or purplish midrib, 10-22 mm long, 20-40 cm in diameter, inner perianth-segments, 8 to12, cream to white usually notched at the apex; outer perianth parts entire to minutely fringed; styles white or greenish; stigma-lobes yellowish to green. The flowers usually are imperfectly unisexual, occurring on functionally dioecious plant, but some plants have flowers that are strictly female, with no stamens.

Blooming Season

Late winter to late spring.

Chromosome Number

2n[44]66.

Radial Spines

10-22, needle-like, straight, white, or in some the tips rose-colored, purplish, brown or black, 4-10 mm long, spreading

Fruits

Scarlet, ovoid to clavate, 10-25 mm long, sticking straight out from the stem, sometimes even remaining when a new round of flowers blooms.