Stenocereus huastecorum, Alvarado-Sizzo & Casas & Parra & Arreola-Nava & Terrazas & Sánchez, 2018

Alvarado-Sizzo, Hernán, Casas, Alejandro, Parra, Fabiola, Arreola-Nava, Hilda Julieta, Terrazas, Teresa & Sánchez, Cristian, 2018, Species delimitation in the Stenocereus griseus (Cactaceae) species complex reveals a new species, S. huastecorum, PLoS ONE (e 0190385) 13 (1), pp. 1-25 : 20

publication ID	https://doi.org/ 10.1371/journal.pone.0190385
DOI	https://doi.org/10.5281/zenodo.12986496
persistent identifier	https://treatment.plazi.org/id/0398344D-FFA0-476A-FDA2-999A42ACFEA1
treatment provided by	Felipe
scientific name	Stenocereus huastecorum
status

Treatment

Stenocereus huastecorum View in CoL , a novel species from northern Mexico

This entity stands as the most cohesive species within the SGSC: its genetic clustering pattern ( Fig 3 View Fig 3 ) is apparent regardless the method used. Ecological ( Fig 5A, 5B, 5G and 5H View Fig 5 ; Table 1 View Table 1 ) and morphological evidence ( Fig 6 View Fig 6 ) shows its uniqueness. Therefore, we consider this group deserves the status of a distinct species given that there is enough genetic, ecological, and morphological evidence to distinguish it from S. griseus (its homonym so far) and S. pruinosus , a supposed sympatric species.

The distributional range of S. huastecorum sp. nov. comprises southern Tamaulipas, western San Luis Potosí, northern Querétaro and Guanajuato as well as disjunctive populations in Veracruz on the south slopes of the Trans-Mexican Volcanic Belt, displaying a distributional gap of 350 km. The distribution area is mainly contained in the Sierra Madre Oriental and the Llanura Costera Nororiental ( Northeastern Coast Plain ) physiographic regions of Mexico, coarsely matching the ethnolinguistic “Huasteca” region after which we name this species.

Summary of species limits and distribution

Every clustering method agreed in major genetic breaks associated with biogeographic regions. We were able to link the range of S. huastecorum with the Llanura Costera Nororiental, Sierra Madre Oriental (Huastecan Karst), and the southern Trans-Mexican Volcanic Belt, which seems to be the strongest genetic barrier when considering the whole complex ( Fig 3 View Fig 3 ). However, this is arguable for S. huastecorum , given that its populations dwell on both North and South of the oldest section of the TMVB (19.5 to 16 Myr), that predates the age of the Core Pachycereeae (Pachycereinae+ Stenocereinae + &chinocereus) at 7 Myr [ 24]. The distribution of S. pruinosus is apparently contained in geologically recent lowlands, Tehuacán Valley and Oaxaca’s Central valleys, surrounded by the Sierra Madre Sur, and it reaches the Pacific Coast through the Oaxaca’s Southern Range, a Miocene volcanic sequence which is also older than the age of the tribe [ 67]. S. laevigatus is separated from S. pruinosus by the biotic barrier of the Isthmus of Tehuantepec [ 22] ( Fig 3 View Fig 3 ) which we identified as a genetic barrier, although not common for the Cactaceae ; [ 24, 25, 68, 69]. The core distribution of S. laevigatus is associated with the Central Depression of Chiapas and the Yucatecan Karst, specifically with the most recent areas of the Yucatán Península which date to barely 18,000 years [ 26] suggesting recent colonization. S. griseus seems to be widespread in Caribbean Coast of North Colombia and Venezuela well as Inter-Andean Valleys, and it is isolated from other SGSC members by the Caribbean Sea and Central America with a singular distributional pattern given that Stenocereus and its relatives are clearly North American [ 24]. Finally to explain both the S. griseus and Antillean S. peruvianus distributions, a more complex, biogeographic hypothesis other than human transport [13] needs to be tested. We observed spatial concordance between biogeographic and genetic barriers, well-known barriers (mainly highlands) such as the Trans-Mexican Volcanic Belt or Sierra Madre del Sur are by far older than the genus Stenocereus , thus being temporally discordant, whereas extant distribution areas are more recent (less than 4 Myr). This odd pattern may suggest that these ranges are soft barriers, with present-day distributions reflecting historical population refugial dynamics [ 70], or strong human effects on the genetic landscape considering that S. pruinosus is a intensively managed resource [ 71]. Demonstrating that one or a combination of these hypotheses will require a time-calibrated phylogeny not only of the SGSC but of the whole genus Stenocereus , as well as a phylogeographic approach within the major lineages.