Mammillaria morentiniana Gonz.-Zam., D. Aquino, J. Mohl & Dan. Sánchez, 2022

González-Zamora, Pedro, Aquino, David, Mohl, Jonathan & Sánchez, Daniel, 2022, A new endemic species of Mammillaria (Cactaceae) from San Luis Potosí, Mexico, Willdenowia 52 (3), pp. 359-372 : 363-366

Mammillaria morentiniana Gonz.-Zam., D. Aquino, J. Mohl & Dan. Sánchez , sp. nov. – Fig. 3.

Holotype: Mexico, San Luis Potosí, Santa María del Río , 2056 m, 28 Aug 2019, P. González-Zamora 11 ( IBUG 215375 ; isotype: SLPM).

Diagnosis — Mammillaria morentiniana is distinguishable from M. bocasana , M. crinita and M. nana by the presence of more than 4 central spines (mean = 5), and differs from M. schwarzii , which presents, on average, 7 thinner central spines (Supplemental content online; Fig. 2). Mammillaria morentiniana bears fewer than 32 straight radial spines (mean = 24.49), whereas M. schwarzii bears more than 32 straight radial spines (mean = 38.98). Mammillaria morentiniana has completely red central spines and black, non-arillate seeds, whereas M. bocasana has red central spines with a yellow base and reddish brown, arillate seeds. Mammillaria morentiniana has glabrous spines and straight radial spines, whereas M. crinita has pubescent spines and tortuous or straight radial spines. Mammillaria morentiniana differs from the sympatric M. nana because the latter has tuberous roots and 0 or 1 pubescent central spines.

Description — Roots slender branched. Stem simple to branched, 2.2–4(–6) cm tall, 1.5–2.6 cm in diam., growth form globose to shortly cylindric, latex watery; tubercles 2–3.5 mm long, 1.5–2.5 mm in diam., axils with tortuous bristles; areoles circular, 0.6–1 mm wide; central spines (3 or)4–6(–8), reddish, acicular, (3.7–)5– 8(–9.4) mm long, glabrous, 1 or 2 of them uncinate; radial spines (17–)19–28(–32), white, acicular, (0.4–)0.5– 0.7(–9.2) mm long, glabrous. Flowers infundibuliform, 7–9 mm long; outer tepals pale yellow with reddish middle stripe, lanceolate, margin entire; inner tepals pale yellow, lanceolate, margin entire; filaments pale yellow; anthers yellow; style pale yellow; stigma pale yellow, 4-lobed. Fruit pink, claviform, 10–20 mm long; seeds black, c. 1.1 mm in diam.; aril absent; testa pitted.

Phenology — Flowering from April to June; fruiting from June to August.

Distribution and habitat — Mammillaria morentiniana is endemic to S San Luis Potosí, Mexico. The species inhabits NW-facing cliffs in a small group of igneous mountains at 1900–2100 m. The vegetation at this elevation is oak forest ( Rzedowski 1978), which is surrounded by xerophytic scrub in the lower zones of the mountains and valleys. Dominant elements of the vegetation are Quercus chihuahuensis Trel. , Q. deserticola Trel. , Dasylirion parryanum Trel. , Beaucarnea hookeri (Lem.) Baker and succulents such as Echinocereus acifer (Salm- Dyck) Lem. , Mammillaria muehlenpfordtii C. F. Först and Pachyphytum hookeri A. Berger.

Conservation — Mammillaria morentiniana is known in only one locality and represents a micro-endemism. Probably, the range-restricted M. morentiniana and M. schwarzii represent relict species with dense spination adapted to previous cold periods and now to winter frosts. We estimate that the population is composed of 250 adult and 150 juvenile plants, occupying an area of c. 0.087 km 2. Following the IUCN Red List categories and criteria ( IUCN Standards and Petitions Committee 2022), we propose M. morentiniana as Critically Endangered, CR B1 ab(iii)+2ab(iii); C1 , based on an EOO of 0.317 km 2 (criterion B1 ) and an AOO of 0.140 km 2 (criterion B2 ). In addition, it is known from only one locality (criteria B1 a and B2 a), presents a poor quality of habitat (criteria B1 b(iii) and B2 b(iii)) and the population size is estimated to number fewer than 250 mature individuals (criterion C1 ) .

Etymology — The specific epithet is dedicated to the Morentín family from Colima, Mexico. Don Marco and Doña Laura spent their lives preserving the flora in W Mexico. They inspired the first author to observe and admire the local and xerophytic flora.

Taxonomic comments — We suggest Mammillaria morentiniana as a part of M. ser. Stylothelae . Members of this series are characterized by having small seeds with spaced testa pits, bristles at the axils, straight central spines and at least one central spine with an uncinate tip ( Hunt & al. 2006). Also, M. morentiniana flowers from April to June like most members of M. ser. Stylothelae ( Butterworth & al. 2007). Mammillaria ser. Stylothelae is distributed in the foothills of the Chihuahuan Desert, Sierra Madre Oriental and Trans-Mexican Volcanic Belt, mainly on igneous soils ( Hernández & Gómez-Hinostrosa 2015). Following Butterworth & al. (2007), deletion of the rpl16 intron is shared by members of M. ser. Stylothelae ( Hunt & al. 2006). Additional analyses are required to confirm the inclusion of M. morentiniana in this series. Despite their superficial similarity, M. morentiniana is distinctive from other close species of M. ser. Stylothelae , by the number of central and radial spines, spine pubescence and seed morphology (see Discussion and Diagnosis). The number of spines, areole dimensions and spine length have been valid for delimiting species in lineages such as Mammillaria ( Zamudio & Guzmán 2017; Ortiz-Brunel & al. 2022), Epithelantha F. A. C. Weber ex Britton & Rose ( Aquino & al. 2019) and Echinocereus Engelm. ( Sánchez & al. 2020). Also, qualitative characteristics such as the presence of tuberous roots, pubescent spines, tortuous spines or a seed aril could provide characters useful for diagnosis. We propose that comprehensive fieldwork and statistical morphological analyses could support a better delimitation of M. ser. Stylothelae . We consider that including M. morentiniana as a part of M. crinita will complicate the taxonomy of the latter species. We end by rephrasing David Hunt (2008), who wrote “please, no more crinita ” to criticize the superspecies concept of M. crinita ( Fitz-Maurice & Fitz-Maurice 2006) .