Frailea Mammifera Hybrid cactus

DFrailea Mammifera Hybrid escription:  F. mammifera  is a  miniature plant, usually solitary, or sometime basally branched.
Stem: It is diminutive in size, subglobose or eventually shortly columnar, glossy dark green and purple, up to 3 cm in height, 2-2,5 cm in diameter.
Ribs: About 17, with round and tapering tubercles.
Areoles: Placed in the upper side of the tubercles.
Central spines: 2-4, erect, golden to brown, stout, 2-3 mm long.
Radial spines: 18-20, spreading, yellowish or whitish, thin, 1,5-2 mm long.
Roots: Fat central tap root.
Flowers: Infundibuliform, larger than the plant itself, sulphur-yellow, 2,5 cm in diameter; tepals abruptly acuminate, long and slender, stigma-lobes 5-7.  But don’t be disappointed when the easily produced buds fail to open.  Fraileas are cleistogamous, meaning that their flowers produce seed without even opening. Without the need for pollination, the buds rarely reach full bloom and remain closed. They will open only in great heat in the hottest, brightest, afternoon sun, if at all.
Fruit: Up to 8 mm in diameter.  Dry,  indehiscent, that detaches easily, pericarp membranous, fragile that break easily, releasing the seed.

Cultivation:  Grow them in rich, porous soil, and let them dry out between waterings.  These plants need a minimum temperature of 5-10° C (but occasionally temperatures of a few degrees below 0° are not dangerous) .
Sun Exposure:  It enjoys full sun, and it can take on a near black appearance when kept in bright light.  In a shaded position the plants grow faster, but are not flat shaped or dark coloured.
Characteristically, during the dry season plants retract completely under the ground, both in the wild and in cultivation too.
Propagation:  With fresh harvested  seeds or (rarely) by grafting.
Notes: This plant is short living (It only lives about 10-15 years).