Name and distribution
POWO accepts Epithelantha micromeris as a species with a natural range from southeastern Arizona to southwestern Texas and northeastern Mexico. Its basionym is Mammillaria micromeris, published in 1856. The current combination dates from 1922. Older broad treatments of E. micromeris also included taxa now recognised as distinct species. [2-WWW]
Mature stem and flowering
The North American description of the nominate subspecies gives a usually solitary, greyish, rough stem 2–3.8 cm in diameter. Areoles have 20–35, locally up to 40 spines in 1–3 rows. Apical spines elongate and then wear away or break. The small flowers are 6–8.5 mm long. At the natural sites covered by this description, flowering occurs in February–April. The flora reports self-pollination. Habitats include gravelly places, rock crevices, desert grasslands and open woodland at 500–1800 m. [Parfitt and Zimmerman 2003, t. 4, p. 239–240, Epithelantha micromeris var. micromeris]
Changes in the appearance of young stems
In the population near Anthony Gap in Texas, Gorelick usually observed stems 15–25 mm in diameter. Smaller pale plants had a smooth spine covering and a concave apex. Larger ones were grey and rough, with a convex apex and buds. The change occurred near a diameter of 15 mm, but applies to this described population. Even small stems had 31–37 spines in one or two series, consistent with identification as E. micromeris. [Gorelick 2026, pp. 1–3]
Different stages were also visible in four stems of one branched specimen. The smaller ones retained a concave apex, and the larger ones produced buds. Two collected individuals, subsequently grown in cultivation, changed into a greyer, rougher form. This material points to an ontogenetic change associated with stem maturation. [Gorelick 2026, pp. 2–4, Fig. 5–9]
In some larger specimens, the author described narrowed peripheral zones, termed stem-collapse rings. He suggested that they were associated with severe dehydration. He also described underground stem sections bearing spines and a taproot with lateral roots. The drawing down of the plant by a contracting root remains an interpretation of the specimen's arrangement. The rate of root shortening and the force moving the stem were not measured in this study. [Gorelick 2026, pp. 4–7]
Habitat diversity
In the study by Aquino and colleagues, E. micromeris occurred in four soil categories and three landforms. These included calcareous desert soils and regosols, and among the landscape forms, karst terrain, plains and former lake beds. Compared with the closely related E. cryptica, climatic data for the sites indicated cooler, drier environments. [Aquino et al. 2021, p. 4524–4527, ryc. 3–4]
The four plastid DNA regions used did not clearly separate E. micromeris and E. cryptica. Recognition of both species also relied on morphological traits and environmental data. The result describes the resolution of these markers within the set of taxa examined. [Aquino et al. 2021, pp. 4525–4527]
Prismatic crystals in the cortex
Scanning microscopy in the 2022 study showed prismatic crystals from the stem cortex of E. micromeris. The analysis formed part of a broader comparison of biomineralisation in Cacteae, covering surface tissues, cortex and pith. The observation identifies a specific mineral form and its location in this species. [De la Rosa-Tilapa et al. 2022, p. 8, ryc. 6I, okaz TT898]
Seeds without detectable lignin
Chen and colleagues detected no lignin in the E. micromeris seeds examined. Thioacidolysis yielded no products characteristic of lignin, and NMR spectra of whole seed walls showed polysaccharide signals without the typical set of signals from this polymer. A similar result was obtained for E. greggii. The chemical characterisation concerns these seeds. Their walls also contain other components. [Chen et al. 2013, pp. 203–206, Fig. 4C]
Narrow areoles and a short flower
Aquino and colleagues compared 25 adult Epithelantha micromeris plants from five sites. In their key, areoles were 0.20–0.30 mm wide and flowers 6–7 mm long. Length covered the whole flower from the base of the pericarpel, the part surrounding the ovary, to the tip of the longest tepal. This measurement has a different meaning from the diameter of an open flower. Areoles were distinctly elongated relative to their width. [Aquino et al. 2019, p. 605, 608, 612, 615; tabela 5]
In the similar E. cryptica, flowers measured 11–12 mm and the oval areoles were wider. The four plastid markers separated these two species poorly, while adding morphological traits allowed both lineages to be recognised. The similarity of the sequences used describes the scope of this marker set. Documented variation in the environments of the sites also supports the plants' distinctness. [Aquino et al. 2019, Aquino et al. 2019, pp. 605–609, 612. Aquino et al. 2021, pp. 4525–4527] [Aquino et al. 2021, Aquino et al. 2019, pp. 605–609, 612. Aquino et al. 2021, pp. 4525–4527]
Related articles
Materials from the author's archive
The species also appears in Konrad Szychowski's private material archive. [Kaktologia 2009b, file p. 8] [Neciu b.d., file p. 1] [Kaktusy i Inne 2005a, file p. 7, 34]
Synonyms and names in the literature
Mammillaria micromeris · Cactus micromeris · Cephalomamillaria micromeris · Epithelantha petri · Cactus leucodasys · Cactus leucodictius · Mammillaria leucodasys · Mammillaria leucodictia [2-WWW]