Epithelantha potosina

Name and distribution

Epithelantha potosina is an accepted species in POWO, native to San Luis Potosí. It was described in 2010 as E. greggii subsp. potosina. The combination at species rank dates from 2019. [2-WWW]

Southerly location and climatic seasonality

E. potosina sites lie at more southerly latitudes than much of the genus's range. In the analysis of climatic data, they were distinguished by lower temperature seasonality and higher isothermality. Isothermality compares daily temperature variation with variation over the year. In this case, it means large seasonal fluctuations are less significant. [Aquino et al. 2021, pp. 4525–4527, Fig. 4]

The comparison of soil categories showed no clear association of E. potosina with one particular category. The plastid DNA tree placed it in a major lineage with E. bokei, E. cryptica, E. ilariae, E. micromeris and E. spinosior. Its position shows a change from its historical placement under E. greggii. [Aquino et al. 2021, p. 4522–4527, ryc. 2–4]

Small areoles above thickened roots

The Epithelantha potosina plants examined had 39–43 spines per areole, areoles 0.50–0.70 mm long and thickened roots. Stems were less than 6.5 cm in diameter. Morphology was analysed in 15 adult plants from three sites in San Luis Potosí. The scanning image of the seed showed the absence of the uneven multicellular sculpturing characteristic of the E. pachyrhiza and E. pulchra material examined. [Aquino et al. 2019, p. 605–606, 610, 612, 615; ryc. 5E, O]

The former name E. greggii subsp. potosina linked this material to E. greggii. In the tree based on four plastid markers, E. potosina belonged to the genus's first major lineage, while E. greggii belonged to the second. Morphological measurements also supported its distinctness. In 2019, the authors published a combination at species rank. Spine counts partly overlap with the range for E. pulchra, so several traits need to be compared together. [Aquino et al. 2019, p. 605–607, 612]

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