Fantastic plants with tiny white spines and bright red fruits.

Family: Cactaceae (Cactus Family)

Scientific Name: Epithelantha micromeris (Engelmann) F.A.C. Weber ex Britt. & Rose 1922
Published in: Bois, Dict. Hort. 2. 804; et ex Britton & Rose, Cactac. 3. 93 (1922), 1898

Common names: Button Cactus, ping-pong ball cactus, Common button cactus

Basionym: Mammillaria micromeris Engelmann, Proc. Amer. Acad. Arts 3: 260. 1856 (as Mamillaria)

Synonyms:

• Epithelantha micromeris var. micromeris (Engelmann) F.A.C. Weber ex Britt. & Rose 1922
• Epithelantha rufispina
• Epithelantha micromeris var. rufispina
• Epithelantha micromeris var. densispina
• Epithelantha densispina Bravo 1951
• Epithelantha spinosior C.Schmoll 1951
• Epithelantha rufispina Bravo 1951
• Cactus micromeris Kuntze 1891
• Mammillaria micromeris 1856

Distribution: USA - Arizona (Santa Cruz and Cochise County) New Mexico (Hildago and Sandoval Co, From Sierra and Chaves to Eddy Co), western Texas. Mexico (northern Chihuahua).
The endemic Mexican taxa have relatively large flowers like those of  E. bokei.

Habitat: Widespread in desert grasslands and woodlands from 500 to 1800m in elevation. It grows on crevices, coarse gravel, cliffs, sedimentary (rarely igneous) substrates on hills and ridges in the Chihuahuan Desert; These cacti are normally found in small clusters because the seeds fall nearby. Also wind, rain, and wildlife help with the dispersal of seeds.
Conservation status: Listed in CITES Appendix II

Etymology: The genus name "Epithelantha" derives from the Greek word “Epi” meaning “upon, on, at, over”;  the Greek word “thele” meaning “nipple”  referring to the tubercles, and “anthos ” meaning “flower” describing flower position near tubercle apex, a reference to the fact that the flowers doesn't originate between the nipple as in the genus Mammillaria. (The genus name implies: “flowers upon the tubercles”).
The species name  "micromeris" means: with small parts or divisions.

Epithelantha micromeris SB125 Arteagas Canyon, Saltillo, Coahuila, Mexico
The rather small flowers are often followed by attractive
red fruits which contrast nicely with the spines.

Description: Miniature globose cactus, erect, unbranched or in small clumps, not deep-seated in substrate, appearing ashy grey and relatively rough in general aspect.
Stem: Unsegmented, mostly spheric or obovoidal, rarely cylindric, often flat-topped with a depressed centre, 1-5(-9)cm tall and up to 2-4 (-7,5) cm in diameter, occasionally more; surface completely obscured by spines; cortex and pith are not mucilaginous.
Tubercles: Numerous, not confluent into ribs, hemispheric or short cylindric, very small, ca. 1-3 mm; arranged in tight spirals around the plant.
Areoles : Small at tips of tubercles, 1 mm long, nearly circular, elliptic when distended by flower or fruit, slightly woolly when young, copiously woolly only at sexually mature stem apex; areolar glands absent;
Spines: 20-35(-40) white to ashy grey 2-5 mm long, appressed on sides of stems, straight, terete, slender, innocuous, in 1-3 superimposed series except for a longer (4-12 mm) and erect adaxial tuft on the top, on sexually mature stem apex often greyish or purplish white, frequently with brown bases, collectively forming brown spots at the centre of each spine cluster. Spine clusters at the sides of stem 4-5(-7) mm in diameter. Smooth or microscopically roughened by break-up of epidermis, not distinguishable as radial and central spines. In fully adult plants, the distal portions of the longest spines are worn, leaving the apex of the plant covered with short, innocuous spines.
Roots: Diffuse (usually) or tap-root (in some populations)  also tuberlike (see: E. pachyriza )
Flower: Inconspicuous, funnelform diurnal, borne at adaxial margins of spine clusters in the plant top. Only partly opened just distal portion visible, as they barely stick out above the wool obscured by longer spines at stem apex. Outer tepals entire or sparsely erose-fimbriate; Inner tepals 5-8 per flower, pink to white (rarely yellow), (1-)2-6(-9) × 3(-5) mm; stamens 15-16; ovary smooth, scales, hairs, and spines absent; stigma lobes (2-)3-4(-6), white, to 1 mm.
Phenology: Flowering late winter-early spring (Feb-Apr)
Fruit: Indehiscent, bright red, thin narrowly cylindric, 3-20 × 2-3(-5) mm, weakly succulent, soon drying and papery, smooth, spineless; pulp absent; floral remnant deciduous. Fruiting late spring-early summer (Apr-Jun).
Seeds: Blackish, obliquely hemispheric reticulated in 0,5mm diameter.

NOTE: Epithelantha micromeris var. micromeris has some of the smallest flowers among cactus species. Unlike other taxa in this genus, it is Autogamous.

Although generally resembling Mammillaria and superficially similar to M. lasiacantha, chloroplast DNA evidence indicates that Epithelantha is taxonomically isolated and more closely related to Pediocactus and Ariocarpus than to Mammillaria.

Cultivation: Although regarded as a choice and difficult plant, in cultivation it is relatively easy. It needs a  particularly well-draining soil mix (rot prone). Water sparingly.
Frost Tolerance: Depending on the variety, will handle -12° C (Temperature Zone: USDA 8-11) Sun Exposure: Light shade to full sun

Propagation: Seeds, offsets .