Thelocactus tepelmemensis T.J. Davis, H.M. Hern., G.D. Starr, and Gómez-Hin., 2018

Davis, Tristan J., Hernández, Héctor M., Starr, Greg D. & Gómez-Hinostrosa, Carlos, 2018, A distinctive new species of Thelocactus (Cactaceae) from Oaxaca, Mexico, Phytotaxa 361 (1), pp. 115-122 : 116-119

Thelocactus tepelmemensis T.J. Davis, H.M. Hern., G.D. Starr, and Gómez-Hin. , sp. nov.

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, hilummicropyle region oval.

Etymology:—The specific name refers to the community of Tepelmeme Villa de Morelos in whose territory the new species is currently known. The suggested English (Tepelmeme cliff cactus) and Spanish (Biznaga de acantilado de Tepelmeme) names refer to the species’ cliff habitat and the community of Tepelmeme Villa de Morelos.

Distribution:—Currently, T. tepelmemensis is known to occur only within a single narrow river canyon in northern Oaxaca, Mexico. Details of the precise location are being withheld to protect the population from illegal activities. The species should be looked for in similar nearby canyons where the specific habitat and exposure are present.

Habitat and Plant Associations:— Thelocactus tepelmemensis was found exclusively on exposed vertical limestone rock in a narrow river gorge in open xerophytic scrub; the limestone had many cracks and small ledges from which the cactus could grow ( Figure 2B ). Smoother, presumably younger portions of the limestone cliffs in the area did not appear to support populations of the cactus.

Additionally, T. tepelmemensis was located almost entirely on east-facing slopes with fewer on northeast and southeast exposed slopes. Seemingly perfect habitat oriented in other directions showed no signs of the new species; this habitat restriction implies that the species cannot tolerate strong sun exposures and only thrives in places where morning sun with some significant shading during the hottest part of each day is available.

Because they were typically located in cracks and on/near small ledges in the cliff face ( Figure 2B ), plants often had accumulated leaf and other vegetative matter in spines and along bases, especially in clumping specimens. In several instances, multiple separate plants were concentrated on ledges or significant gaps where seeds could accumulate.

The plant was recorded from 1420 m to 1460 m elevation in dry xerophytic scrub. Associated plants on the slopes included: Agave titanota Gentry (1982: 176) ( Asparagaceae ); Hechtia spp. , Tillandsia spp. ( Bromeliaceae ); Bursera spp. ( Burseraceae ); Cephalocereus columna-trajani (Karwinsky in Pfeiffer 1837: 76) K. Schumann (1897: 198), Opuntia pubescens H.L. Wendland in Pfeiffer (1837: 149), Opuntia decumbens Salm-Dyck (1834: 361) , Escontria chiotilla (F.A.C. Weber in Schumann 1897: 83) Rose (1906: 126), Mammillaria carnea Zuccarini in Pfeiffer (1837: 19), Mammillaria albilanata Backeberg (1939: 47) , Mammillaria viperina J.A. Purpus (1912: 148) , Pilosocereus chrysacanthus (F.A.C. Weber in Schumann 1897: 178) Byles & G.D. Rowley (1957: 66), Stenocereus sp. ( Cactaceae ); Sedum sp. ( Crassulaceae ); Cnidoscolus multilobus (Pax in Engler 1910: 107) I.M. Johnston (1923: 86) ( Euphorbiaceae ); Acacia spp. ( Fabaceae ); Fouquieria purpusii Brandegee (1909: 386) ( Fouquieriaceae ); and, Selaginella lepidophylla ( Hooker & Greville 1830: 162) Spring (1840: 126) ( Selaginellaceae ).

Phenology:—Primary flowering seems to occur from December through February, which is the dry season in the area. Flowering was recorded January 17, 2018 with most plants with at least one flower open and all but a few with at least developing flower buds. At that time, few plants had spent flowers from the current season. The species was also recorded blooming February 6–8, 2017; however, most flowering seemed done at that time with most plants showing spent flower remains, few developing flower buds, and limited evidence of mature fruits. Plants as small as 4 cm diam. showed developing buds or spent flowers. A small iridescent hymenopteran was seen emerging from a mature flower in February 2017. Several immature fruits and one mature fruit were preserved in January 2018; only one mature fruit was noted in February 2017 but not preserved. Seed set probably occurs most commonly in March through May, which is the start of the rainy season in the area. Local inhabitants indicate flowering and fruiting occurred throughout the year.

Figures

FIGURE 1. Thelocactus tepelmemensis. A. Stem with flower. B. Areoles. C. Flower (lateral view and dissected). D. Fruit. Voucher: H.M. Hernández et al. 4128 (MEXU). Drawn by Albino Luna.

FIGURE 2. Thelocactus tepelmemensis (body, flower, and fruit) and its habitat. A. Caespitose individual with several lateral stems (Type). B. Vertical limestone wall with several individuals. C. External aspect of a flower (above); dissected flower showing the internal perianth segments, the stamens, and the gynoecium (middle); and, semi-mature fruit with persistent perianth (below). Voucher: H.M. Hernández et al. 4128 (MEXU).

FIGURE 3. Scanning Electron Microscope (SEM) micrographs of Thelocactus tepelmemensis seeds. A. Lateral view. B. Dorsal view showing the keel. C. View of the hilum-micropyle region (the arrow indicates the position of the micropyle). D. Detail showing cell shape and microrelief. Voucher: H.M. Hernández et al. 4128 (MEXU).