Epithelantha pachyrhiza

Name and distribution

Epithelantha pachyrhiza is a species native to Coahuila in POWO. The current combination was published in 1954 (formerly E. micromeris var. pachyrhiza, and in some later treatments subsp. pachyrhiza). The former subsp. pulchra is now the distinct species E. pulchra. [2-WWW]

Substrate and site locations

In the 2021 spatial study, E. pachyrhiza was associated with calcaric xerosols and the foothill zone. The categories refer to soil and topography from the maps used for the georeferenced sites. For these two traits, the excess of observed sites over expected frequency was clear in the contingency-table analysis. [Aquino et al. 2021, pp. 4524–4525, Fig. 3]

In the tree based on four plastid DNA regions, the species formed part of a major lineage with E. greggii, E. polycephala and E. pulchra. The present separation of E. pachyrhiza and E. pulchra allows environmental results to be assigned separately to the two species studied. [Aquino et al. 2021, Aquino et al., pp. 4522–4525, fig. 2. POWO, as of 11 October 2026] [2-WWW]

Thickened roots and elliptical areoles

Epithelantha pachyrhiza has thickened roots and elliptical areoles. In the 2019 key, it was identified by its white spines and areoles 0.45–0.55 mm wide. The material directly measured and sequenced was identified as E. pachyrhiza subsp. parvula, now a synonym of E. pachyrhiza. It included ten adult plants from two sites. It had 16–21 spines per areole. [Aquino et al. 2019, pp. 601, 605, 608, 611–612, POWO synonyms, as of 11 October 2026] [2-WWW]

Material formerly termed the nominate subspecies and subsp. elongata was included in the same species on the basis of earlier descriptions and comparison of traits, because these plants were not obtained for sequencing. Spine counts reported in the literature for these groups were higher and partly overlapped. Elliptical areoles remained a shared trait. The measurement range for parvula material thus describes a specific part of the accepted species. [Aquino et al. 2019, p. 601, 611]

Seed-coat sculpturing

Uneven sculpturing spanning many cells and expansions on the sides of the hilum region were visible on seeds of the material examined. Similar seed traits occurred in E. pulchra. The species differed in spine number and areole shape and occupied separate positions in the plastid tree. In the analysis, E. pachyrhiza was closer to E. polycephala, while E. pulchra grouped with E. greggii. [Aquino et al. 2019, p. 607–611; ryc. 3–5J, M–N]

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