Xerophyte

Central Spines

2, rarely 4-6, much longer and stouter than the radials, slightly diverging, light purplish, bluish brown or black, subulate, straight or sometimes tortuous, upper one erect, others diverging, 10-25 mm long.

Seeds

Curved-pear-shaped, brown, 1-1.2 mm long.

Description

Mammillaria johnstoniiSN|32831]]SN|32831]] is large for the genus, usually solitary but occasionally clustering basally, eventually 15 to 20 cm high. Flowers white to pale pink to cream, with pink to brownish midveins, to 20 mm in diameter.

Tubercles

1 to 1.5 cm long, 6-9 mm broad at base, 4-angled throughout, in 13 and 21 spirals, somewhat bluish, juice milky, naked in their axils, milky.

Flowers

From near top of plant but from axils of old tubercles, campanulate, 1.5-2 cm long, outer perianth-segments ovate-lanceolate, acute to obtuse, greenish white to pinkish green with a reddish-brown mid-rib, margins ciliate to serrate. Inner perianth-segments narrow, acuminate, white, pink to brownish with white to cream margins. Filaments short, pink above, cream below. Style pinkish. Stigma-lobes linear, 6 or 7, olive-green.

Stem

Globular to short-oblong, dull bluish gray-green, 15 to 20 cm high and 10 cm in diameter, slightly depressed at apex.

Radial Spines

10 to 14(-18), white to horn-colored with, but with brown or black tips, stiff-acicular, straight, somewhat spreading, slightly ascending, 6-9 mm long.

Fruits

Globose to clavate, swollen, scarlet, about 2.5 cm long.

Areoles

Spine-areoles when young short-floccose, in age glabrate, circular.