Thelocactus tepelmemensis T.J. Davis, H.M. Hern., G.D. Starr, and Gómez-Hin., Phytotaxa 361: 116 (2018).

   Diagnosis: Similar to Thelocactus leucacanthus, but differing in having a lower number of spines per areole, these being poorly differentiated into radials and centrals (vs. more and readily differentiated spines); by the much smaller, red-purple flowers (vs. larger yellow or magenta flowers); and, the conjunct seed micropyle lying inside the hilum border (vs. disjunct micropyle lying outside border).

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)

Stems solitary or caespitose with up to 11 (rarely more) lateral stems, usually erect, depressed-globose, globose to cylindrical, glabrous, to 14(—30.5) cm tall, 10.5 cm diam., green, not obscured by the spines. Ribs (11—)13, tuberculate, vertical, rounded apically. Areoles circular to elliptic, usually developing a rectangular or triangular groove at the proximal side, 3—4 mm diam. in the widest portion, 5—8(—10) mm long including the groove, 15—20(—25) mm apart, with white or tan wool; 2—3 small glands rarely present proximally in flowering areoles. Spines acicular, (6—)8—9 per areole, poorly differentiated, radiating but usually with one spine centrally located, diffuse to erect, straight, rounded in cross section, rigid, moderately piercing at touch, reddish or tan with reddish tips when young, becoming grey with age, of unequal length, 1—2.6(—4.2) cm long, 0.47—0.84(—1.1) mm diam. at base. Flowers arising from the stem apex at the proximal portion of the areoles of young tubercles, infundibuliform, diurnal, 1.3—2.3 cm long at anthesis; pericarp covered with scales, greenish or reddish; scales deltoid or widely ovate, truncate or sub-auriculate at base, fimbriate at margin, apiculate, 0.5—1 mm long, white with reddish or pinkish centers. Perianth segments membranous, red-purple with pink or white margins; external segments ovate-lanceolate becoming lanceolate towards the flower apex, fimbriate at margin, acute or apiculate apically, 4—9 mm long × 2—3 mm wide; internal segments lanceolate, entire at margin, acute or apiculate apically, 10—11 mm long × 2—3 mm wide. Stamens numerous, erect; filaments white, of unequal length, 3—5 mm long, variably inserted near to well-above the nectary, with the lower filaments arising ca. 3 mm above the base of the tube; anthers yellow; ovary obovate, truncate apically, ca. 2 mm long × 1.8 mm wide; style greenish-white, cylindric, 7—9 mm long × 0.7 mm wide; stigma lobate, with 6 radiating 0.5—0.6 mm long lobes. Fruits ovoid, scaly, red-purple at maturity, with the perianth persistent, non-fleshy, to 1 × 0.5 cm. Seeds broadly oval, medium-sized, 1.06—1.21 mm long × 0.78—1 mm wide, semi-matt, black-brown, periphery keeled; border expanded around hilum; cells polygonal, gradually smaller towards hilum, isodiametric, anticlinal boundaries raised, straight; microrelief finely verrucose; hilum large, basal, impressed, micropyle conjunct lying inside the hilum border, hilum-micropyle region oval.