Epithelantha micromeris Origin and Habitat: 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 Epithelantha bokei.
Altitude: It grows from 500 to 1800 metres in elevation.
Habitat and Ecology: Widespread in desert grasslands and woodlands It grows on crevices, coarse gravel, cliffs, sedimentary calcareous rock (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. The species has an exceptionally large range, high number of individuals and low threat, therefore it is listed as Least Concern.
Epithelantha micromeris Description: Epithelantha micromeris is a 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 low, ca. 1(-3) mm long 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. The upper radials on the young tubercles longer and connivent over the apex, narrowly clavate, the upper half finally falling off. 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: Epithelantha 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.
Blooming season:: Flowers late winter-early spring (Feb-Apr).
Fruits: 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 0,5-1,5 mm diameter.