The genus Thelocactus 

Type: MEXICO. Oaxaca, municipality Tepelmeme, 17 January 2018 (fl., fr.), H.M. Hernández et al. 4128 (holotype: MEXU 1471315!; isotypes: DES!, MEXU 1471316!). (Figures 1—3)


Description
Stem single or clustering, globose to elongate, 14(-30.5) cm tall, 10.5 cm wide. Ribs (11-)13, distinct. Tubercles rounded. Areoles with 3 small glands rarely present. Spines (6-)8-9, 10-26(-42) mm long, poorly differentiated, radiating but usually with one spine centrally located, diffuse to erect, straight, rounded in cross section, reddish or tan. Flowers 13-23 mm long at anthesis, red-purple. Seeds 1.06-1.21 x 0.78-1 mm, testa cells tabular with a finely verrucose microrelief.

Distribution
Mexico, Oaxaca, occurring in a narrow river canyon on vertical limestone rock in open xerophitic scrub.

Risk assessment
Thelocactus tepelmemensis has a limited known distribution and a small population size, therefore it has been suggested to consider this species as Vulnerable.

Comments
The epithet refers to the community of Tepelmeme Villa de Morelos in whose territory the species is found.