Introduction

The Chihuahuan Desert biogeographic province is situated in the Mexican Plateau, in northern and central Mexico, and southwestern United States of America (^{Challenger, 1988}; ^{Morrone, 2019}). Since its recognition by ^{Shreve (1942)}, it has been analyzed by many authors under different biogeographic approaches. When we examine these analyses and try to integrate them, however, one nomenclatural problem is obvious: different authors have applied different names to this province, e.g., Chihuahuan province (^{Dice, 1943}), Chihuahua-Zacatecas province (^{Goldman & Moore, 1945}), Plateau province (^{Rzedowski, 1978}) and Mexican Plateau province (^{Campbell, 1999}). Furthermore, smaller areas have been recognized with the same names, e.g., Chihuahuan province (^{Smith, 1941}), Chihuahuan district (^{Cabrera & Willink, 1973}), Chihuahuan subregion (^{Hafner & Riddle, 2005}), Chihuahuan Desert area (^{Muldavin, 2002}) and Chihuahuan Desert region (^{Sosa et al., 2018}), being sometimes unclear when an author using the names “Chihuahuan Desert” or “Chihuahuan” refers to the same or different biogeographic units. This unnecessary nomenclatural confusion should be put to an end and a uniform nomenclature applied.

In addition to this nomenclatural proliferation, the recognition of smaller areas nested within the Chihuahuan Desert province deserves to be analyzed. Authors have recognized ecoregions, regions, districts, provinces, subprovinces, areas and zones, which in some cases refer to the same biogeographic unit. Thus, it seems important to find out which areas are subordinated to this province and which are their valid names.

Our objective is to analyze the areas previously recognized in the Chihuahuan Desert province and the names applied to them, and to identify the taxa that are endemic to them. We provide a biogeographic regionalization and a uniform nomenclature, applying the International Code of Area Nomenclature or ICAN (^{Ebach et al., 2008}).

Materials and methods

Published regionalizations were compared, looking for their similarities and differences, and especially considering the maps presented by the authors. Additionally, papers analyzing plant and animal taxa distributed in the Chihuahuan Desert area were considered to identify potential endemic species to diagnose the areas. A comparison of the units recognized within the area corresponding to the Chihuahuan Desert province showed a set of 5 smaller units subordinated to 2 larger ones. As the whole area has been considered to represent a biogeographic province and applying the International Code of Area Nomenclature (^{Ebach et al., 2008}), we treated the largest units as subprovinces and the smallest ones as districts. We searched in the literature (e.g., monographs, systematic revisions, faunistic and floristic analyses, etc.) and databases for endemic species that diagnose these biotic units. The valid names of the different units are assigned following the International Code of Area Nomenclature (^{Ebach et al., 2008}). Endemic species for each unit are listed alphabetically.

Results

Chihuahuan Desert province

Chihuahuan Desert area ^{Shreve, 1942: 235}; ^{Morafka et al., 1992: 195}.

Chihuahuan province ^{Dice, 1943: 58} (non ^{Smith, 1941}); ^{Dasmann, 1973: 30}; ^{Udvardy, 1975: 17}; ^{Brown et al., 1998: 118}; ^{Rojas et al., 2013: 274}. Chihuahua-Zacatecas province ^{Goldman and Moore, 1945: 354}; ^{Stuart, 1964: 350}.

Chihuahuan Desert province ^{Moore, 1945: 218}; ^{Casas-Andreu and Reyna-Trujillo, 1990: map}; ^{Gadsden et al., 2006: 117}; ^{Rojas et al., 2013: 274}; ^{Gámez et al., 2017: 12}; ^{Morrone et al., 2017: 278}; ^{Morrone, 2019: 28; Myers et al., 2019: 211}; ^{Ocampo-Salinas et al., 2019: 9}.

Chihuahuan zone ^{Rzedowski, 1973: 64}.

Plateau province ^{Rzedowski, 1978: 106}; ^{Challenger, 1988: 646}; ^{Rzedowski and Reyna-Trujillo, 1990: map}.

Mexican Plateau province ^{Campbell, 1999: 115}; ^{Morrone, 2001: 22}, ^{2005: 232}; ^{Escalante et al., 2013: 495}.

Chihuahuan Desert region ^{Hafner and Riddle, 2005: 227}; ^{Villarreal-Quintanilla et al., 2017: 66}; ^{Majure et al., 2019: 1337}.

North American Hot Deserts ecoregion ^{Challenger and Soberón, 2008: 103 (in part)}.

Definition. The Chihuahuan Desert province is one of the desert or dry areas assigned to the Nearctic region. It is clearly separated from similar areas, e.g., the Great Basin, Mojave and Sonoran deserts, by the Sierra Madre Occidental and the Rocky Mountains. ^{Shreve (1942)} considered that 2 areas situated south of the Chihuahuan desert, the Mezquital and the Tehuacán-Cuicatlán Valleys, represented lesser extreme types of deserts, but harbored all the life-forms present in the Chihuahuan and Sonoran deserts. ^{Rzedowski (1973)} also recognized that the Mezquital and Tehuacán-Cuicatlán Valleys had strong floristic similarities with the Chihuahuan Desert. We propose herein a broadened circumscription of the Chihuahuan Desert province, by assigning these southern areas to it, as also supported by molecular analyses of rodent species (^{Fernández, 2012}; ^{Fernández et al., 2012}) and sclerophyllous Rosaceae (^{Vázquez-Cruz et al., 2019}).

The name Chihuahuan Desert has historical precedence over Chihuahuan, which additionally has been used by ^{Smith (1941)} for a smaller unit nested within this province. The names Chihuahuan-Zacatecas (^{Goldman & Moore, 1945}), Plateau (^{Rzedowski, 1978}) and Mexican Plateau province (^{Campbell, 1999}) are equivalent to the Chihuahuan Desert province.

Subprovinces. Different authors have recognized units within this province (^{Smith, 1941}; ^{Morafka, 1977}; ^{Ramírez-Pulido & Castro-Campillo, 1990}; ^{Dinerstein et al., 1995}; ^{Arriaga et al., 1997}; ^{Hafner & Riddle, 2005}; ^{Espinosa-Organista et al., 2008}; ^{Morrone, 2019}). Considering the Chihuahuan Desert in its broadest extension, namely including the Tehuacán-Cuicatlán Valley, the 5 smaller units recognized are grouped herein in 2 subprovinces: the Chihuahuan subprovince in the north and the Mexican Plateau subprovince in the south (^{Arriaga et al., 1997}; ^{Morrone, 2019}; ^{Ocampo-Salinas et al., 2019}).

Chihuahuan subprovince, stat. nov.

Chihuahuan region ^{Cooper, 1859: 269}.

Coahuilan region ^{Cooper, 1859: 269}.

Chihuahuan province ^{Smith, 1941: 100}.

Mesa del Norte region ^{West, 1964: 368}.

Chihuahuan district ^{Cabrera and Willink, 1973: 35}.

Chihuahuan Xeric Scrub ecoregion ^{Dinerstein et al., 1995: 104 (in part)} .

Northern Plateau (Chihuahuan) province ^{Arriaga et al., 1997: 61}.

Chihuahua Desert, N province ^{Escalante et al., 1998: 284}.

Chihuahuan subregion ^{Hafner and Riddle, 2005: 227}; ^{Riddle and Hafner, 2006: 438}; ^{Neiswenter et al., 2019: 1848}.

Chihuahuan Desert area ^{Muldavin, 2002: 453}; ^{Vázquez-Cruz and Sosa, 2019: 446}.

Northern Plateau (Chihuahuan Desert) province ^{Espinosa-Organista et al., 2008: 60}.

Coahuilan district ^{Morrone, 2019: 28}.

Chihuahuan Desert region ^{Sosa et al., 2018: 524}.

Northern Chihuahuan Desert area ^{Ocampo Salinas et al., 2019: 15}.

Definition. It corresponds to the northernmost part of the province and includes the Trans-Pecos and Mapimian districts (Fig. 1).

Figure 1 Biogeographic subprovinces and districts of the Chihuahuan Desert province. 

Endemic taxa. Abelia coriacea var. subcoriacea (Caprifoliaceae; ^{Villarreal-Quintanilla et al., 2017}). Acacia angustissima var. chisosiana and A. schottii (Fabaceae; ^{Villarreal-Quintanilla et al., 2017}). Acleisanthes chenopodioides (Nyctaginaceae; ^{Villarreal-Quintanilla et al., 2017}). Agave parrasana (Asparagaceae; ^{Villarreal-Quintanilla et al., 2017}). Agonum extimum (Carabidae; ^{Ball & Shpeley, 2000}; ^{Bousquet, 2012}; ^{Conabio, 2020}). Allolepis texana (Poaceae; ^{Royo et al., 2014}; ^{Conabio, 2020}). Ammospermophilus interpres (Sciuridae; ^{Best et al., 1990}; ^{Timm et al., 2016}). Andrena trimaculata (Andrenidae; ^{Ayala et al., 1996}). Anisacanthus linearis (Acanthaceae; ^{Villarreal-Quintanilla et al., 2017}). Anulocaulis eriosolenus (Nyctaginaceae; ^{Villarreal-Quintanilla et al., 2017}). Arenaria ludens (Caryophyllaceae; ^{Villarreal-Quintanilla et al., 2017}). Argemone chisosensis (Papaveraceae; ^{Villarreal-Quintanilla et al., 2017}). Argoporis craigi and A. durangoensis (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Ariocarpus fissuratus fissuratus (Cactaceae; ^{González-Elizondo et al., 2017b}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Asbolus mexicanus mexicanus (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Astragalus emoryanus var. terlinguensis (Fabaceae; ^{Villarreal-Quintanilla et al., 2017}). Bembidion impotens and B. durangoense (Carabidae; ^{Bousquet, 2012}; ^{Ball & Shpeley, 2000}; ^{Conabio, 2020}). Blapstinus palmeri (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Blepharidachne bigelovii (Poaceae; ^{Villarreal-Quintanilla et al., 2017}). Bonamia multicaulis (Convolvulaceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Bouchea linifolia and B. spathulata var. spathulata (Verbenaceae; ^{Villarreal-Quintanilla et al., 2017}). Bouteloua breviseta, B. erecta and B. warnockii (Poaceae; ^{Programa de Manejo Área de Protección de Flora y Fauna Médanos de Samalayuca, 2013}; ^{Villarreal-Quintanilla et al., 2017}). Brickellia glutinosa and B. urolepis (Asteraceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Brongniartia minutifolia (Fabaceae; ^{Villarreal-Quintanilla et al., 2017}). Calliopsis coloratipes, C. australior, C. rozeni, C. squamifera and C. meliloti (Andrenidae; ^{Ayala et al., 1996}). Carabus forreri forreri (Carabidae; ^{Bousquet, 2012}). Carlowrightia mexicana (Acanthaceae; ^{Villarreal-Quintanilla et al., 2017}). Chaetopappa plomoensis and Ch. pulchella (Asteraceae; ^{Royo & Melgoza-Castillo, 2014a}, ^b; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Cicindela obsoleta santaclarae and C. hornii hornii (Carabidae; ^{Bousquet, 2012}). Corynopuntia aggeria and C. bulbispina (Cactaceae; ^{González-Elizondo et al., 2017b}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Coryphantha compacta, C. delaetiana, C. gracilis, C. longicornis, C. poselgeriana and C. ramillosa subsp. ramillosa (Cactaceae; ^{Lebgue-Keleng et al., 2014}; ^{Royo & Melgoza-Castillo, 2014a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Cotinis rufipennis (Melolonthidae; ^{Morón, 1996}; ^{Deloya & Ratcliffe, 1988}; ^{Conabio, 2020}). Croton sancti-lazari (Euphorbiaceae; ^{Villarreal-Quintanilla et al., 2017}). Cylindera debilis (Carabidae; ^{Bousquet, 2012}). Cylindropuntia kleiniae (Cactaceae; ^{Villarreal-Quintanilla et al., 2017}). Cyprinodon macrolepis (Cyprinodontidae; ^{Rodríguez-Pineda et al., 2014}; ^{Conabio, 2020}). Dalea neo-mexicana var. megaladenia (Fabaceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Dalquestia concho (Sclerosomatidae; ^{Kury & Cokendolpher, 2000}; ^{Conabio, 2020}). Dendrocoris neomexicanus and D. reticulatus (Lygaeidae; ^{Slater & Brailosvsky, 2000}; ^{Conabio, 2020}). Derobrachus lepesmei (Cerambycidae; ^{Noguera & Chemsak, 1996}; ^{Conabio, 2020}). Diplotaxis belfragei, D. boops, D. catarinas and D. completa (Melolonthidae; ^{Morón 1996}; ^{Conabio, 2020}). Dipodomys nelsoni (Heteromyidae; ^{Best, 1988}; ^{Álvarez-Castañeda et al., 2016a}). Drymaria coahuilana and D. pachyphylla (Caryophyllaceae; ^{Royo et al., 2014}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Echinocereus adustus, E. longisetus subsp. longisetus and E. palmeri (Cactaceae; ^{Lebgue-Keleng et al., 2014}; ^{González-Elizondo et al., 2017a}, ^b; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Echinomastus intertextus, E. mariposensis and E. warnockii (Cactaceae; ^{Lebgue-Keleng et al., 2014}; ^{Royo et al., 2014}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Eleodes forreri, E. rugosifrons and E. thomasi (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}). Emorya suaveolens (Cactaceae; ^{Villarreal-Quintanilla et al., 2017}). Eriocampidea arizonensis (Tenthredinidae; ^{Pérez-Santiago et al., 2017}). Erigeron coronariusnull (Asteraceae; Royo & Melgoza-Castillo, 2014d; ^{Conabio, 2020}). Escobaria chihuahuensis and E. tuberculosa subsp. tuberculosa (Cactaceae; ^{Lebgue-Keleng et al., 2014}; ^{Royo & Melgoza-Castillo, 2014a}; ^{Royo et al., 2014}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Escobaria henricksonii (Cactaceae; ^{González-Elizondo et al., 2017b}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Euphorbia exstipulata and E. theriaca (Euphorbiaceae; ^{Villarreal-Quintanilla et al., 2017}). Euodynerus tempiferus subsp. tempiferus (Vespidae; ^{Rodríguez-Palafox, 1996}; ^{Conabio, 2000}). Eusattus pons (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Exomalopsis levigata (Apidae; ^{Ayala et al., 1996}). Fagonia scoparia (Zygophyllaceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Royo et al., 2014}; ^{Conabio, 2020}). Festuca ligulata (Poaceae; ^{Villarreal-Quintanilla et al., 2017}). Flourensia pulcherrima (Poaceae; ^{Villarreal-Quintanilla et al., 2017}). Flyriella parryi (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Fouquieria shrevei (Fouqueriaceae; ^{Royo et al., 2014}; ^{Conabio, 2020}). Galium carmenicola and G. mexicanum subsp. flexicum (Rubiaceae; ^{Villarreal-Quintanilla et al., 2017}). Genistidium dumosum (Fabaceae; ^{Villarreal-Quintanilla et al., 2017}). Grusonia bradtiana (Cactaceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Conabio, 2020}). Gundlachia triantha (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Halimolobos diffusa (Brassicaceae; ^{Villarreal-Quintanilla et al., 2017}). Heliotropium molle (Boraginaceae; ^{Villarreal-Quintanilla et al., 2017}). Helops spilmani (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Hexalectris warnockii (Orchidaceae; ^{Villarreal-Quintanilla et al., 2017}). Justicia warnockii (Acanthaceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Laothoe junglandis (Sphingidae; ^{León-Cortéz, 2000}; ^{Conabio, 2020}). Leiobunum townsendi (Sclerosomatidae; ^{Kury & Cokendolpher, 2000}; ^{Conabio, 2020}). Leucophyllum alejandrae (Scrophulariaceae; ^{Villarreal-Quintanilla et al., 2017}). Leucosyris turneri (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Lycium puberulum var. puberulum (Solanaceae; ^{Villarreal-Quintanilla et al., 2017}). Mabrya erecta (Plantaginaceae; ^{Villarreal-Quintanilla et al., 2017}). Malaxis wendtii (Orchidaceae; ^{Villarreal-Quintanilla et al., 2017}). Mammillaria grusonii, M. pennispinosa subsp. nazasensis and M. zeyeriana (Cactaceae; ^{Lebgue-Keleng et al., 2014}; ^{Royo & Melgoza-Castillo, 2014a}; ^{Royo et al., 2014}; ^{González-Elizondo et al., 2017b}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Martinapis luteicornis (Apidae; ^{Ayala et al., 1996}; ^{Conabio, 2020}). Melica montezumae (Poaceae; ^{Villarreal-Quintanilla et al., 2017}). Mentzelia saxicola (Loasaceae ^{Villarreal-Quintanilla et al., 2017}). Mexalictus micheneri (Halictidae; ^{Ayala et al., 1996}). Milla bryanii (Asparagaceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Muhlenbergia setifolia (Poaceae; ^{Villarreal-Quintanilla et al., 2017}). Nama havardii (Boraginaceae; ^{Villarreal-Quintanilla et al., 2017}). Nerisyrenia castillonii and N. gypsophila (Brassicaceae; ^{Villarreal-Quintanilla et al., 2017}). Nomada graciana (Apidae; ^{Ayala et al., 1996}). Notholaena neglecta (Pteridaceae; ^{Villarreal-Quintanilla et al., 2017}). Packera millelobata (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Pectis incisifolia (Asteraceae; ^{Royo & Melgoza-Castillo, 2014a}, ^b; ^{Conabio, 2020}). Pelecyphorus dispar, P. liratus and P. obliviosus (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Perityle parryi and P. vaseyi (Asteraceae ^{Villarreal-Quintanilla et al., 2017}). Phacelia petiolata (Boraginaceae; ^{Villarreal-Quintanilla et al., 2017}). Phyllanthopsis arida (Euphorbiaceae; ^{Villarreal-Quintanilla et al., 2017}). Physaria mcvaughiana and P. mexicana (Brassicaceae; ^{Villarreal-Quintanilla et al., 2017}). Plateilema palmeri (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Pleopeltis riograndensis (Polypodiaceae; Villarreal-Quintanilla, 2001). Podolasia rotundipenis (Scarabaeidae; ^{Morón 1996}; ^{Howden, 1997}; ^{Conabio, 2020}). Polistes comanchus subsp. comanchus (Vespidae; ^{Rodríguez-Palafox, 1996}; Conabio, 2000). Polygala nudata (Polygalaceae; ^{Villarreal-Quintanilla et al., 2017}). Prionus curticollis (Cerambycidae; ^{Noguera & Chemsak, 1996}; ^{Conabio, 2020}). Psilostrophe gnaphalodes var. mexicana and P. tagetina (Asteraceae; ^{Programa de Manejo Área de Protección de Flora y Fauna Médanos de Samalayuca, 2013}; ^{Royo & Melgoza-Castillo, 2014b}; ^{Conabio, 2020}). Prunus havardii (Rosaceae; ^{Villarreal-Quintanilla et al., 2017}). Psathyrotopsis scaposa (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Pseudoclappia arenaria (Asteraceae ^{Villarreal-Quintanilla et al., 2017}). Quercus coahuilensis, Q. gravesii and Q. pungens (Fagaceae; ^{Villarreal-Quintanilla et al., 2017}). Rorippa ramosa (Brassicaceae; ^{Villarreal-Quintanilla et al., 2017}). Ruellia parryi (Acanthaceae; ^{Villarreal-Quintanilla et al., 2017}). Sartwellia gypsophila and S. puberula (Asteraceae; Royo & Melgoza-Castillo, 2014d; ^{Conabio, 2020}). Sceloporus bimaculosus and S. merriami (Phrynosomatidae; ^{Olsen, 1979}; ^{Hammerson et al., 2007}; ^{Lemos-Espinal et al., 2018}; ^{Hernández et al., 2019}). Selaginella viridissima (Selaginellaceae; ^{Villarreal-Quintanilla et al., 2017}). Senna monozyx and S. pilosior (Fabaceae; ^{Villarreal-Quintanilla et al., 2017}). Seymeria falcata var. falcata and S. falcata var. uncinata (Orobanchaceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Sida longipes (Malvaceae; ^{Villarreal-Quintanilla et al., 2017}). Solanum leptosepalum (Solanaceae; ^{Villarreal-Quintanilla et al., 2017}). Stenandrium barbatum (Acanthaceae; ^{Villarreal-Quintanilla et al., 2017}). Stenodynerus perblandus (Vespidae; ^{Rodríguez-Palafox, 1996}; ^{Conabio, 2020}). Stenomorpha segregata, S. evertissima, S. furcata, S. geminata and S. immunda (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Steriphanus lentus (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Thelocactus heterochromus (Cactaceae; ^{Lebgue-Keleng et al., 2014}). Tidestromia carnosa, T. suffruticosa var. coahuilana and T. suffruticosa var. suffruticosa (Amaranthaceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Royo et al., 2014}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Tiquilia gossypina (Boraginaceae; ^{Villarreal-Quintanilla et al., 2017}). Trachemys gaigeae (Emydidae; ^{Iverson, 1992}; ^{Ernst & Lovich, 2009}; ^{van Dijk, 2011}). Tradescantia wrightii (Commelinaceae; ^{Villarreal-Quintanilla et al., 2017}). Triorophus lecontei (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Typhlusechus spilmani (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Viguiera phenax (Asteraceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Royo et al., 2014}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Xenelmis sandersoni (Elmidae; ^{Conabio, 2020}; Santiago-Fragoso & Spangler, 2000). Xenoglossa patricia (Apidae; ^{Ayala et al., 1996}). Xylorhiza wrightii (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Xylothamia purpusiinull (Asteraceae; Royo & Melgoza-Castillo, 2014d; ^{Conabio, 2020}). Yucca elata (Asparagaceae; ^{Programa de Manejo Área de Protección de Flora y Fauna Médanos de Samalayuca, 2013}). Zacosmia maculata subsp. maculata (Apidae; ^{Ayala et al., 1996}). Zinnia oligantha (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Zootermopsis laticeps (Archotermopsidae; ^{Cancello & Myles, 2000}; ^{Conabio, 2020}).

Trans-Pecos district, stat. nov.

Trans-Pecos subprovince ^{Morafka, 1977: 198}; ^{Díaz-Cárdenas et al., 2019: 864}; ^{Myers et al., 2019: 211}.

Chihuahuan province ^{Ferrusquía-Villafranca, 1990: map} (non ^{Smith, 1941} nec ^{Dice, 1943}); ^{Ramírez-Pulido and Castro-Campillo, 1990: map}.

Coahuilan province ^{Ferrusquía-Villafranca, 1990: map}; ^{Ramírez-Pulido and Castro-Campillo, 1990: map}.

Mexican Interior Chaparral ecoregion ^{Dinerstein et al., 1995: 104}.

Trans-Pecos subregion ^{Hafner and Riddle, 2005: 227}; ^{Riddle and Hafner, 2006: 438}; ^{Neiswenter et al., 2019: 1848}.

Trans-Pecos region ^{Hassenflu et al., 2017: 902}; ^{Scheinvar et al., 2017: 324}; ^{Duran and Roman, 2019: 126}.

Definition. This district corresponds to the northernmost part of the subprovince, in southern New Mexico and Texas (^{Morafka, 1977}). ^{Muldavin (2002)} analyzed the northern boundary of the Chihuahuan Desert province, which also corresponds to the northern boundary of the Trans-Pecos district, evaluating the distributional ranges of ca. 500 plant species.

Endemic taxa. Abies durangensis var. coahuilensis (Pinaceae; ^{Villarreal-Quintanilla et al., 2017}). Acleisanthes parvifolia and A. wrightii (Nyctaginaceae; ^{Villarreal-Quintanilla et al., 2017}). Agastache cana (Lamiaceae; ^{Villarreal-Quintanilla et al., 2017}). Agave havardiana (Asparagaceae; ^{Villarreal-Quintanilla et al., 2017}). Allium coryi and A. perdulce var. sperryi (Amaryllidaceae; ^{Villarreal-Quintanilla et al., 2017}). Amsonia arenaria and A. tharpii (Apocynaceae; ^{Villarreal-Quintanilla et al., 2017}). Ancistrocactus scheeri (Cactaceae; ^{Villarreal-Quintanilla et al., 2017}). Anomiopsyllus nudatus mexicanus (Ctenophthalmidae; ^{Holland, 1965}). Anulocaulis leiosolenus var. gypsogenus, A. leiosolenus var. howardii, A. leiosolenus var. lasianthus and A. reflexus (Nyctaginaceae; ^{Villarreal-Quintanilla et al., 2017}). Argemone brevicornuta and A. turnerae var. ownbeyana (Papaveraceae; ^{Villarreal-Quintanilla et al., 2017}). Aristolochia coryi (Aristolochiaceae; ^{Villarreal-Quintanilla et al., 2017}). Aspidoscelis exanguis and A. tesselata (Teiidae; ^{Stuart, 1991}; ^{Walker et al., 1997}; ^{Hammerson et al., 2007}, ²⁰¹⁹). Astragalus mollissimus var. marcidus (Fabaceae; ^{Villarreal-Quintanilla et al., 2017}). Astranthium robustum (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Bonamia ovalifolia (Convolvulaceae; ^{Villarreal-Quintanilla et al., 2017}). Bouchea spathulata var. longiflora (Verbenaceae; ^{Villarreal-Quintanilla et al., 2017}). Bouteloua chihuahuana and B. kayi (Poaceae; ^{Royo et al., 2014}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Brickellia laccata, B. lemmonii var. carmenensis and B. stolonifera (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Calosoma haydeni haydeni (Carabidae; ^{Bousquet, 2012}). Carlowrightia lesueurii (Acanthaceae; ^{Villarreal-Quintanilla et al., 2017}). Casnonia lengi (Carabidae; ^{Bousquet, 2012}). Castilleja wootonii (Orobanchaceae; ^{Villarreal-Quintanilla et al., 2017}). Chaetopappa hersheyi (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Choisya dumosa (Rutaceae; ^{Villarreal-Quintanilla et al., 2017}). Cirsium turneri (Asteraceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Conabio, 2020}). Cleomella longipes (Capparaceae; ^{Villarreal-Quintanilla et al., 2017}). Cordylanthus wrightii ssp. tenuifolius (Scrophulariaceae; ^{Programa de Manejo Área de Protección de Flora y Fauna Médanos de Samalayuca, 2013}; ^{Royo & Melgoza-Castillo, 2014a}; ^{Conabio, 2020}). Corynopuntia schottii (Cactaceae; ^{Villarreal-Quintanilla et al., 2017}). Coryphantha echinus, C. hesteri, C. mínima, C. ramillosa subsp. santarosa, C. robbinsorum and C. robustispina subsp. scheeri (Cactaceae; ^{Villarreal-Quintanilla et al., 2017}). Crataegus tracyi var. coahuilensis (Rosaceae; ^{Villarreal-Quintanilla et al., 2017}). Cratogeomys castanops (Geomyidae; ^{Davidow-Henry et al., 1989}; ^{Hafner et al., 2008}; ^{Cassola, 2016a}). Cryptantha cinerea var. laxa and C. crassipes (Boraginaceae; ^{Villarreal-Quintanilla et al., 2017}). Cylindropuntia imbricata subsp. argentea (Cactaceae; ^{Villarreal-Quintanilla et al., 2017}). Cymopterus filifolius (Apiaceae; ^{Villarreal-Quintanilla et al., 2017}). Dalea bartonii and D. janosensis (Fabaceae; ^{Vega-Mares et al., 2014}; ^{Villarreal-Quintanilla et al., 2017}). Dipodomys elator (Heteromyidae; ^{Carter et al., 1985}; ^{Jones et al., 1988}; ^{Wahle et al., 2018}). Donnellsmithia coahuilensis (Apiaceae; ^{Villarreal-Quintanilla et al., 2017}). Drymaria coahuilana and D. pratheri (Caryophyllaceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Echinocereus chisoensis subsp. chisoensis, E. dasyacanthus, E. davisii, E. parryi, E. russanthus subsp. feehnii, E. viridiflorus subsp. chloranthus, E. viridiflorus subsp. correllii and E. viridiflorus subsp. cylindricus (Cactaceae; ^{Programa de Manejo Área de Protección de Flora y Fauna Médanos de Samalayuca, 2013}; ^{Lebgue-Keleng et al., 2014}; ^{Royo & Melgoza-Castillo, 2014a}; ^{Conabio, 2020}; ^{Villarreal-Quintanilla et al., 2017}). Echinomastus intertextus subsp. dasyacanthus (Cactaceae; ^{Villarreal-Quintanilla et al., 2017}). Eleodes carbonaria nuevoleonensis, E. easterlai, E. striolata and E. tenuipes (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}). Emorya rinconensis (Cactaceae; ^{Villarreal-Quintanilla et al., 2017}). Epithelantha cryptica and E. micromeris subsp. bokei (Cactaceae; ^{Villarreal-Quintanilla et al., 2017}). Eragrostis erosa (Poaceae; ^{Villarreal-Quintanilla et al., 2017}). Eriogonum atrorubens var. rupestre, E. gypsophilum, E. havardii, E. hemipterum var. griseum, E. hemipterum var. hemipterum, E. jamesii var. undulatum and E. suffruticosum (Polygonaceae; ^{Villarreal-Quintanilla et al., 2017}). Escobaria albicolumnaria, E. dasyacantha subsp. dasyacantha, E. duncanii, E. orcuttii and E. sneedii subsp. sneedii (Cactaceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Euphorbia geyeri var. wheelerianase, E. henricksonii, E. ivanjohnstonii, E. perennans, E. simulans and E. theriaca var. theriaca (Euphorbiaceae; ^{Royo et al., 2014}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Fryxellia pygmaea (Malvaceae; ^{Villarreal-Quintanilla et al., 2017}). Gaillardia turneri (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Gaura macrocarpa (Onagraceae; ^{Villarreal-Quintanilla et al., 2017}). Geomys arenarius and G. knoxjonesi (Geomyidae; ^{Hafner & Geluso, 1983}; ^{Hopton & Cameron, 2001}; ^{Frey, 2004}; ^{Cassola, 2016b}; ^{Lacher et al., 2019}). Grindelia havardii (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Habroscelimorpha fulgoris fulgoris (Carabidae; ^{Bousquet, 2012}). Hedeoma chihuahuensis, H. johnstonii, H. mollis and H. pilosa (Lamiaceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Helenium chihuahuensis (Asteraceae; ^{Carreón-Hernández, 2014}; ^{Royo & Melgoza-Castillo, 2014a}; ^{Conabio, 2020}). Helianthus neglectus and H. paradoxus (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Ipomopsis wendtii (Polemoniaceae; ^{Villarreal-Quintanilla et al., 2017}). Kallstroemia perennans (Zygophyllaceae; ^{Villarreal-Quintanilla et al., 2017}). Lechea mensalis (Cistaceae; ^{Villarreal-Quintanilla et al., 2017}). Lepidospartum burgessii (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Linum allredii and L. vernale (Linaceae; ^{Villarreal-Quintanilla et al., 2017}). Lobelia anatina var. riskindii (Campanulaceae; ^{Villarreal-Quintanilla et al., 2017}). Lycium puberulum var. berberioides and L. texanum (Solanaceae; ^{Villarreal-Quintanilla et al., 2017}). Mammillaria wrightii subsp. wrightii (Cactaceae; ^{Royo et al., 2014}; ^{Conabio, 2020}). Matelea chihuahuensis and M. texensis (Apocynaceae; ^{Vega-Mares et al., 2014}; ^{Villarreal-Quintanilla et al., 2017}). Mentzelia humilis var. guadalupensis (Loasaceae; ^{Villarreal-Quintanilla et al., 2017}). Nama havardii, N. torynophylla and N. xylopoda (Boraginaceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Nerisyrenia hypercorax (Brassicaceae; ^{Villarreal-Quintanilla et al., 2017}). Nesaea longipes (Lythraceae; ^{Villarreal-Quintanilla et al., 2017}). Nolina arenicola (Aspargace; ^{Villarreal-Quintanilla et al., 2017}). Omphalodes chiangii (Boraginaceae; ^{Villarreal-Quintanilla et al., 2017}). Opuntia arenaria, O. atrispina, O. aureispina, O. chisosensis and O. spinosibacca (Cactaceae; ^{Programa de Manejo Área de Protección de Flora y Fauna Médanos de Samalayuca, 2013}; ^{Lebgue-Keleng et al., 2014}; ^{Villarreal-Quintanilla et al., 2017}). Paronychia wilkinsonii (Caryophyllaceae; ^{Villarreal-Quintanilla et al., 2017}). Perityle bisetosa var. appressa, P. bisetosa var. scalaris, P. bisetosa var. spathulata, P. carmenensis, P. castillonii, P. dissecta, P. fosteri, P. huecoensis, P. rupestris var. albiflora, P. var. rupestris and P. vitreomontana (Asteraceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Phacelia carmenensis and P. intermedia (Boraginaceae; ^{Villarreal-Quintanilla et al., 2017}). Phemeranthus brevicaulis (Portulacaceae; ^{Villarreal-Quintanilla et al., 2017}). Phyllanthus ericoides (Euphorbiaceae; ^{Villarreal-Quintanilla et al., 2017}). Philolithus elatus elatus (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Physaria johnstonii and P. wyndii (Brassicaceae; ^{Villarreal-Quintanilla et al., 2017}). Pinaropappus parvus var. parvus and P. powellii (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Poa wendtii (Poacea; ^{Villarreal-Quintanilla et al., 2017}). Poliomintha maderensis (Lamiaceae; ^{Villarreal-Quintanilla et al., 2017}). Polygala maravillensis and P. rimulicola var. mescalerorum (Polygalaceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Proboscidea sabulosa and P. spicata (Martyniaceae; ^{Royo et al., 2014}; ^{Villarreal-Quintanilla et al., 2017}). Porophyllum greggii (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Potamogeton clystocarpus (Potamogetonaceae; ^{Villarreal-Quintanilla et al., 2017}). Prunus murrayana (Rosaceae; ^{Villarreal-Quintanilla et al., 2017}). Pseudoclappia watsonii (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Quercus carmenensis, Q. deliquescens, Q. hinckleyi and Q. robusta (Fagaceae; ^{Villarreal-Quintanilla et al., 2017}). Raphanorhyncha crassa (Brassicaceae; ^{Villarreal-Quintanilla et al., 2017}). Rosa woodsii var. maderensis (Rosaceae; ^{Villarreal-Quintanilla et al., 2017}). Salvia vinacea (Lamiaceae; ^{Villarreal-Quintanilla et al., 2017}). Scaphinotus biedermani, S. elevatus neomexicanus, S. petersi corvus and S. petersi kathleenae (Carabidae; ^{Bousquet, 2012}). Scutellaria laevis and S. wendtii (Lamiaceae; ^{Villarreal-Quintanilla et al., 2017}). Selaginella macrathera, S. mutica var. limitanea and S. x neomexicana (Selaginellaceae; ^{Villarreal-Quintanilla et al., 2017}). Solanum davisense and S. fendleri var. texense (Solanaceae; ^{Villarreal-Quintanilla et al., 2017}). Sophora arizonica var. gypsophila (Fabaceae; ^{Villarreal-Quintanilla et al., 2017}). Sartwellia gypsophila (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Senecio riskindii and S. warnockii (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Stenaria butterwickiae (Rubiaceae; ^{Villarreal-Quintanilla et al., 2017}). Stenomorpha obliterata and S. mancipata (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Stevia ovata var. texana (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Streptanthus cutleri and S. platycarpus (Brassicaceae; ^{Villarreal-Quintanilla et al., 2017}). Thelocactus bicolor subsp. flavidispinus (Cactaceae; ^{Villarreal-Quintanilla et al., 2017}). Thelesperma subaequale (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Thelypodium texanum (Brassicaceae; ^{Villarreal-Quintanilla et al., 2017}). Trimorphodon vilkinsonii (Colubridae; ^{LaDuc & Johnson, 2003}; ^{Frost et al., 2007}). Triorophus nodiceps (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Yucca campestris and Y. faxoniana (Asparagaceae; ^{Royo & Melgoza-Castillo, 2014a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Zeltnera maryanniana (Gentianaceae; ^{Villarreal-Quintanilla et al., 2017}).

Mapimian district, stat. nov.

Mapimi province ^{Kendeigh, 1961: 273}.

Mapimiam province ^{Hagmeier, 1966: 290}.

Mapimian subprovince ^{Morafka, 1977: 199}; ^{Gadsden et al., 2006: 117}; ^{Vázquez-Cruz and Sosa, 2016: 1698}; ^{Díaz-Cárdenas et al., 2019: 864}; ^{Myers et al., 2019: 211}.

Plateau province ^{Ferrusquía-Villafranca, 1990: map (in part)}.

Zacatecan province ^{Ramírez-Pulido and Castro-Campillo, 1990: map (in part)}.

Coahuilan subregion ^{Hafner and Riddle, 2005: 227}; ^{Riddle and Hafner, 2006: 438}; ^{Neiswenter et al., 2019: 1848}.

Mapimian region ^{Scheinvar et al., 2017: 324}.

Definition. This district corresponds to the southern portion of the subprovince, in southeastern Chihuahua, Coahuila and northeastern Durango (^{Morafka, 1977}; ^{Díaz-Cárdenas et al., 2019}).

Endemic taxa. Abutilon coahuilae (Malvaceae; ^{Villarreal-Quintanilla et al., 2017}). Acleisanthes palmeri and A. purpusiana var. purpusiana (Nyctaginaceae; ^{Villarreal-Quintanilla et al., 2017}). Acharagma aguirreana (Cactaceae; ^{Villarreal-Quintanilla et al., 2017}). Acourtia durangensis (Asteraceae; ^{González-Elizondo et al., 2017a}; ^{Conabio, 2020}). Agave asperrima subsp. maderensis, A. asperrima subsp. zarcensis, A. nickelsii, A. pintilla, A. victoriae-reginae subsp. swobodae and A. victoriaereginae subsp. victoria-reginae (Asparagaceae; ^{González-Elizondo et al., 2017a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Ageratina flourensifolia and A. glischra (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Allium huntiae and A. mannii (Amaryllidaceae; ^{González-Elizondo et al., 2017a}; ^{Conabio, 2020}). Amaranthus acanthobracteatus (Amaranthaceae; ^{Villarreal-Quintanilla et al., 2017}). Ambrosia johnstoniorum (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Andrena mexicana, A. pectidis and A. verbesinae (Andrenidae; ^{Ayala et al., 1996}; ^{Conabio, 2020}). Aneflus obscurus (Cerambycidae; ^{Noguera & Chemsak, 1996}). Anomiopsyllus durangoensis, A. nidophilus and A. nudatus hiemalis (Ctenophthalmidae; Vargas, 1951; ^{Holland, 1965}; ^{Tipton & Méndez, 1968}; ^{Barnes et al., 1977}; ^{Ayala-Barajas et al., 1988}). Antiphytum hintoniorum (Boraginaceae; ^{Villarreal-Quintanilla et al., 2017}). Anulocaulis hintoniorum (Nyctaginaceae; ^{Villarreal-Quintanilla et al., 2017}). Arenaria hintoniorum (Caryophyllaceae; ^{Villarreal-Quintanilla et al., 2017}). Argemone fruticosa (Papaveraceae; ^{Villarreal-Quintanilla et al., 2017}). Astragalus pomphocalyx and A. rupertii (Fabaceae; ^{Villarreal-Quintanilla et al., 2017}). Astrophytum capricorne, A. coahuilense and A. myriostigma subsp. coahuilense (Cactaceae; ^{González-Elizondo et al., 2017a}, ^b; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Atactorhynchus duranguensis (Neoechinorhynchidae; ^{Salgado-Maldonado et al., 2005}; ^{Pérez-Ponce de León & Aguilar-Aguilar, 2019}). Atriplex acanthocarpa subsp. stewartii, A. prosopidium, A. reptans and A. monilifera (Chenopodiaceae; ^{Villarreal-Quintanilla et al., 2017}). Batesimalva lobata (Malvaceae; ^{Villarreal-Quintanilla et al., 2017}). Berberis pinifolia var. coahuilensis (Berberidaceae; ^{Villarreal-Quintanilla et al., 2017}). Blepharida variegatus (Chrysomelidae; ^{Ordóñez-Reséndiz, 2014}; ^{Conabio 2020}). Bouteloua eriostachya and B. johnstonii (Poaceae; ^{Villarreal-Quintanilla et al., 2017}). Brickellia gentryi (Asteraceae; ^{González-Elizondo et al., 2017a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Brongniartia riesebergii (Fabaceae; ^{González-Elizondo et al., 2017a}; ^{Conabio, 2020}). Bromus pinetorum (Poaceae; ^{Villarreal-Quintanilla et al., 2017}). Calanticaria brevifolia, C. inegii and C. oligantha (Asteraceae; ^{González-Elizondo et al., 2017a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Canotia wendtii (Celastraceae; ^{Villarreal-Quintanilla et al., 2017}). Carex gypsophila (Cyperaceae; ^{Villarreal-Quintanilla et al., 2017}). Carlowrightia ovata and C. parvifolia (Acanthaceae; ^{Villarreal-Quintanilla et al., 2017}). Cephalodynerus sculleni (Vespidae; ^{Rodríguez-Palafox, 1996}; ^{Conabio 2020}). Clematis coahuilensis (Ranunculaceae; ^{Villarreal-Quintanilla et al., 2017}). Clinopodium maderense (Lamiaceae; ^{Villarreal-Quintanilla et al., 2017}). Cnidoscolus shrevei (Euphorbiaceae; ^{Villarreal-Quintanilla et al., 2017}). Comarostaphylis polifolia subsp. coahuilensis (Ericaceae; ^{Villarreal-Quintanilla et al., 2017}). Curculio durangoensis (Curculionidae; ^{Conabio, 2020}). Chaboissaea subbiflora (Poaceae; ^{Herrera & Cortés, 2009}; ^{González-Elizondo et al., 2017a}; ^{Conabio, 2020}). Chaetodipus durangae (Heteromyidae; ^{Neiswenter et al., 2019}). Chaetopappa parryi (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Chamaesaracha geohintonii (Solanaceae; ^{Villarreal-Quintanilla et al., 2017}). Championa suturalis (Cerambycidae; ^{Noguera & Chemsak, 1996}). Chiococca henricksonii (Rubiaceae; ^{Villarreal-Quintanilla et al., 2017}). Chinquipellobunus coahuilaensis (Stygnopsidae; ^{Cokendolpher, 2004}). Coryphantha clavata subsp. clavata, C. difficilis, C. durangensis, C. gracilis, C. hintoniorum, C. longicornis, C. kracikii, C. pseudonickelsiae, C. pseudoechinus subsp. laui, C. pseudoechinus subsp. pseudoechinus, C. recurvata canatlanensis, C. unicornis and C. werdermannii (Cactaceae; ^{Lebgue-Keleng et al., 2014}; ^{Royo & Melgoza-Castillo, 2014a}; ^{González-Elizondo et al., 2017a}, ^b; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Corynopuntia grahamii and C. moelleri (Cactaceae; ^{González-Elizondo et al., 2017b}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Cotinus chiangii (Anacardiaceae; ^{González-Elizondo et al., 2017a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Coursetia insomniifolia (Fabaceae; ^{Villarreal-Quintanilla et al., 2017}). Coutaportla pailensis (Rubiaceae; ^{Villarreal-Quintanilla et al., 2017}). Crataegus johnstonii (Rosaceae; ^{Villarreal-Quintanilla et al., 2017}). Cryptantha geohintonii and C. gypsites (Boraginaceae; ^{Villarreal-Quintanilla et al., 2017}). Cylindropuntia anteojoensis (Cactaceae; ^{Villarreal-Quintanilla et al., 2017}). Cypringlea coahuilensis (Cyperaceae; ^{Villarreal-Quintanilla et al., 2017}). Dalea conetensis, D. melantha var. pubens, D. rupertii, D. transiens and D. urceolata lucida (Fabaceae; ^{Estrada et al., 2003}, ²⁰¹¹; ^{González-Elizondo et al., 2017a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Dandya purpusii (Asparagaceae; ^{Villarreal-Quintanilla et al., 2017}). Dasylirion simplex (Nolinaceae; ^{González-Elizondo et al., 2017a}). Dermatophyllum purpusii (Fabaceae; ^{Villarreal-Quintanilla et al., 2017}). Diplotaxis atratula and D. contracta (Melolonthidae; ^{Morón, 1996}; ^{Conabio, 2020}). Drymaria axillaris, D. barkleyi, D. elata, D. jenniferae, D. lyropetala var. coahuilana, D. subumbellata and D. suffruticosa (Caryophyllaceae; ^{Villarreal-Quintanilla et al., 2017}). Dryopetalon paysonii (Brassicaceae; ^{Villarreal-Quintanilla et al., 2017}). Dysphania stellata (Chenopodiaceae; ^{Villarreal-Quintanilla et al., 2017}). Echeveria turgida (Crassulaceae; ^{Villarreal-Quintanilla et al., 2017}). Echinocereus chisoensis var. fobeanus, E. longisetus subsp. delaetii, E. nivosus, E. primolanatus, E. schereri and E. stramineus occidentalis (Cactaceae; ^{González-Elizondo et al., 2017a}, ^b; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Echinomastus unguispinus subsp. minimus and E. unguispinus subsp. unguispinus (Cactaceae; ^{Lebgue-Keleng et al., 2014}; ^{González-Elizondo et al., 2017a}, ^b; ^{Conabio, 2020}). Echinopterys setosa (Malpighiaceae; ^{Villarreal-Quintanilla et al., 2017}). Eleocharis gonzaleziae (Cyperaceae; ^{González-Elizondo et al., 2017a}). Eleodes bidens, E. longicornis, E. peropaca and E. punctigera (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}). Elytroleptus humeralis (Cerambycidae; ^{Noguera & Chemsak, 1996}). Epithelantha micromeris subsp. greggii, E. micromeris subsp. pachyrhiza and E. micromeris subsp. polycephala (Cactaceae; ^{Villarreal-Quintanilla et al., 2017}). Erigeron cuatrocienegensis, E. mimus, E. chiangii and E. heleniae (Asteraceae; ^{González-Elizondo et al., 2017a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Eriogonum fimbriatum, E. henricksonii and E. turneri (Polygonaceae; ^{Villarreal-Quintanilla et al., 2017}). Escobaria laredoi and E. zilziana (Cactaceae; ^{Villarreal-Quintanilla et al., 2017}). Eucnide durangensis (Loasaceae; ^{Villarreal-Quintanilla et al., 2017}). Euphorbia correllii, E. crepitata var. crepitata, E. crepitata var. longa, E. cressoides, E. fruticulosa var. fruticulosa, E. fruticulosa var. hirtella, E. neilmuellerii and E. pinkavana (Euphorbiaceae; ^{Villarreal-Quintanilla et al., 2017}). Eusattus obliteratus and E. cienegus (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Eustoma barkley (Gentianaceae; ^{Villarreal-Quintanilla et al., 2017}). Fagonia scoparia (Zygophyllaceae; ^{Villarreal-Quintanilla et al., 2017}). Flaveria intermedia and F. palmeri (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Flourensia ilicifolia, F. microphylla, F. retinophylla and F. solitaria (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Fouquieria splendens campanulata and F. shrevei (Fouquieriaceae; ^{González-Elizondo et al., 2017a}; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Gaillardia candelaria var. candelaria, G. candelaria var. mikemoorei, G. henricksonii and G. powellii (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Gentianella loongicollis (Gentianaceae; ^{González-Elizondo et al., 2017a}; Villarreal-Quintanilla et al., 2009). Giliastrum purpusii (Polemoniaceae; ^{Villarreal-Quintanilla et al., 2017}). Glandularia alejandrana (Verbenaceae; ^{Villarreal-Quintanilla et al., 2017}). Gopherus flavomarginatus (Testudinidae; ^{Truett & Phillips, 2009}; ^{Kiester et al., 2018}). Grusonia bradtiana (Cactaceae; ^{González-Elizondo et al., 2017b}; ^{Villarreal-Quintanilla et al., 2017}). Halimolobos elatus (Brassicaceae; ^{González-Elizondo et al., 2017a}; ^{Conabio, 2020}). Haplidus pubescens (Cerambycidae; ^{Noguera & Chemsak, 1996}). Haploesthes fruticosa, H. hintoniana and H. robusta (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Hechtia mapimiana (Bromeliaceae; ^{González-Elizondo et al., 2017a}). Hedeoma irvingii and H. montana (Lamiaceae; ^{Villarreal-Quintanilla et al., 2017}). Hedyotis teretifolia (Rubiaceae; ^{Villarreal-Quintanilla et al., 2017}). Helops longicornis, H. spiethi and H. spissicornis (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Henricksonia mexicana (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Holographis ilicifolia (Acanthaceae; ^{Villarreal-Quintanilla et al., 2017}). Hylocrinus subapterus (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Hymenorus durangoensis and H. forreri (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Ipomoea zimmermanii (Convolvulaceae; ^{Villarreal-Quintanilla et al., 2017}). Justicia coahuilana and J. decurvata (Acanthaceae; ^{Villarreal-Quintanilla et al., 2017}). Kinosternon durangoensis (Kinosternidae; ^{Serb et al., 2001}; ^{van Dijk, 2007}). Lenophyllum weinbergii (Crassulaceae; ^{Villarreal-Quintanilla et al., 2017}). Lepturges subglaber (Cerambycidae; ^{Noguera & Chemsak, 1996}; ^{Conabio 2020}). Leucophyllum coahuilensis (Scrophulariaceae; ^{Villarreal-Quintanilla et al., 2017}). Libellula coahuiltecana (Libellulidae; ^{Ortega-Salas & González-Soriano, 2019}). Ligictaluridus pricei (Dactylogyridae; ^{Mendoza-Garfias et al., 2017}). Lithospermum jimulcense (Boraginaceae; ^{Villarreal-Quintanilla et al., 2017}). Lobelia henricksonii (Campanulaceae; ^{Villarreal-Quintanilla et al., 2017}). Lycium arochae (Solanaceae; ^{Villarreal-Quintanilla et al., 2017}). Mabrya coccinea (Plantaginaceae; ^{Villarreal-Quintanilla et al., 2017}). Machaeranthera restiformis (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Machaonia pringlei (Rubiaceae; ^{Villarreal-Quintanilla et al., 2017}). Mammillaria carretii, M. coahuilensis subsp. albiarmata, M. coahuilensis subsp. coahuilensis, M. chionocephala, M. guelzowiana, M. lenta, M. longiflora longiflora, M. magallanii, M. pachycylindrica, M. parrasensis, M. pennispinosa brachytrichion, M. pennispinosa nazasensis, M. pennispinosa pennispinosa, M. saboae roczekii, M. stella-de-tacubaya and M. theresae (Cactaceae; ^{Lebgue-Keleng et al., 2014}; ^{González-Elizondo et al., 2017a}, ^b; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio, 2020}). Manfreda brunnea (Asparagaceae; ^{Villarreal-Quintanilla et al., 2017}). Mesadenus chiangii (Orchidaceae; ^{Villarreal-Quintanilla et al., 2017}). Marshalljohnstonia gypsophila (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Matelea greggii (Apocynaceae; ^{González-Elizondo et al., 2017a}; ^{Conabio, 2020}). Maurandya antirrhiniflora subsp. hederifolia (Plantaginaceae; ^{Villarreal-Quintanilla et al., 2017}). Megacorax gracielanus (Onagraceae; ^{González-Elizondo et al., 2017a}; ^{Conabio, 2020}). Menodora hintoniorum (Oleaceae; ^{Villarreal-Quintanilla et al., 2017}). Mesadenus chiangii (Orchidaceae; ^{Villarreal-Quintanilla et al., 2017}). Methia dentata (Cerambycidae; ^{Noguera & Chemsak, 1996}). Microphallus opacus coahuila (Microphallidae; ^{Pérez-Ponce de León & Aguilar-Aguilar, 2019}). Mortonia latisepala (Celastraceae; ^{Villarreal-Quintanilla et al., 2017}). Muhlenbergia michisensis, M. pubigluma and M. subbiflora (Poaceae; ^{Herrera & Cortés, 2009}; ^{González-Elizondo et al., 2017a}; ^{Herrera-Arrieta & Heynes Silerio, 2017}; ^{Conabio, 2020}). Nama constancei, N. cuatrocienegensis, N. flavescens, N. johnstonii and N. serpylloides var. velutina (Boraginaceae; ^{Villarreal-Quintanilla et al., 2017}). Nerisyrenia incana, N. johnstonii and N. linearifolia var. baconiana (Brassicaceae; ^{Villarreal-Quintanilla et al., 2017}). Nomada durangoae and N. saltillo (Apidae; ^{Ayala et al., 1996}). Omphalodes carranzae (Boraginaceae; ^{Villarreal-Quintanilla et al., 2017}). Opuntia pailana and O. x carstenii (Cactaceae; ^{Villarreal-Quintanilla et al., 2017}). Paronychia albomarginata (Caryophyllaceae; ^{Villarreal-Quintanilla et al., 2017}). Paruroctonus coahuilanus (Vaejovidae; ^{Haradon, 1985}; ^{Conabio, 2020}; ^{Lourenço & Sissom, 2000}). Pectis incisifolia and P. pringlei (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Pelecyphorus bibasalis, P. hebes, P. planatulus and P. undatus (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Pelidnotopsis plusiotina (Melolonthidae; ^{Morón, 1996}; ^{Conabio, 2020}). Penstemon henricksonii and P. punctatus (Plantaginaceae; ^{Villarreal-Quintanilla et al., 2017}). Perityle coahuilensis (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Petalonyx crenatus (Loasaceae; ^{Villarreal-Quintanilla et al., 2017}). Phacelia hintoniorum and P. pallida (Boraginaceae; ^{Villarreal-Quintanilla et al., 2017}). Phaseolus plagiocylix (Fabaceae; ^{Villarreal-Quintanilla et al., 2017}). Philolithus ingens (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Phyllanthus fraguensis (Euphorbiaceae; ^{Villarreal-Quintanilla et al., 2017}). Pinaropappus mojadanus (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Piptochaetium brevicalyx flexuosum (Poaceae; ^{González-Elizondo et al., 2017a}; ^{Conabio, 2020}). Poa matrioccidentalis matri-occidentalis (Poaceae; ^{González-Elizondo et al., 2017a}; ^{Conabio, 2020}). Podisus neglectus (Lygaeidae; ^{Slater & Brailosvsky, 2000}; ^{Conabio, 2020}). Podolasia diabla and P. parapilosa (Scarabaeidae; ^{Andrew et al., 2017}). Pogonocherus arizonicus (Cerambycidae; ^{Noguera & Chemsak, 1996}; ^{Conabio 2020}). Polygala parrasana and P. viridis (Polygalaceae; ^{Villarreal-Quintanilla et al., 2017}). Poliomintha dendritica (Lamiaceae; ^{Villarreal-Quintanilla et al., 2017}). Pomaria fruticosa (Fabaceae; ^{Villarreal-Quintanilla et al., 2017}). Porophyllum amplexicaule (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Prionus batesi and P. howdeni (Cerambycidae; ^{Noguera & Chemsak, 1996}; ^{Santos-Silva et al., 2016}). Prunus cercocarpifolia (Rosaceae; ^{Villarreal-Quintanilla et al., 2017}). Psathyrotopsis hintoniorum and P. purpusii (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Pseudomasaris cazieri (Vespidae; ^{Rodríguez-Palafox, 1996}; ^{Conabio, 2020}). Pseudouroctonus chicano (Vaejovidae; ^{Lourenço & Sissom, 2000}). Quercus invaginata and Q. saltillensis (Fagaceae; ^{Villarreal-Quintanilla et al., 2017}). Randia pringlei (Rubiaceae; ^{Villarreal-Quintanilla et al., 2017}). Rhamnus standleyana (Rhamnaceae; ^{Villarreal-Quintanilla et al., 2017}). Rollinsia paysonii (Brassicaceae; ^{Villarreal-Quintanilla et al., 2017}). Ruellia jimulcensis (Acanthaceae; ^{Villarreal-Quintanilla et al., 2017}). Sabatia tuberculata (Gentianaceae; ^{Villarreal-Quintanilla et al., 2017}). Salvia chionophylla, S. coahuilensis, S. jessicae, S. lanicalyx, S. monclovensis, S. pseudopallida and S. purpusii (Lamiaceae; ^{Villarreal-Quintanilla et al., 2017}). Samolus dichondrifolius and S. ebracteatus var. coahuilensis (Primulaceae; ^{Villarreal-Quintanilla et al., 2017}). Seymeria coahuilana and S. pailana (Orobanchaceae; ^{Villarreal-Quintanilla et al., 2017}). Senna ripleyana (Fabaceae; ^{Royo et al., 2014}; ^{Conabio, 2020}). Simanthedon linsleyi (Apidae; ^{Ayala et al., 1996}; ^{Conabio, 2020}). Siphonoglossa durangensis (Acanthaceae; ^{Villarreal-Quintanilla et al., 2017}). Sphaerocardamum compressum (Brassicaceae; ^{Villarreal-Quintanilla et al., 2017}). Sphaeralcea reflexa (Malvaceae; ^{Villarreal-Quintanilla et al., 2017}). Sphecodosoma beameri (Apidae; ^{Ayala et al., 1996}; ^{Conabio, 2020}). Sphenophorus charlesi (Curculionidae; ^{Morrone & Cuevas, 2004}; ^{Conabio 2020}). Solanum johnstonii (Solanaceae; ^{Villarreal-Quintanilla et al., 2017}). Sporobolus airoides subsp. regis and S. coahuilensis (Poacea; Herrera-Arrieta & Heynes-Silerio, 2017; ^{Villarreal-Quintanilla et al., 2017}; ^{Conabio 2020}). Senecio claryae (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Solidago ericamerioides (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Stenaria mullerae (Rubiaceae; ^{Villarreal-Quintanilla et al., 2017}). Stenelmis occidentalis (Elmidae; ^{Santiago-Fragoso & Spangler, 2000}; ^{Conabio, 2020}). Stenocactus multicostatus subsp. multicostatus and S. multicostatus subsp. zacatecasensis (Cactaceae; ^{González-Elizondo et al., 2017b}; ^{Villarreal-Quintanilla et al., 2017}). Stenomorpha durangoensis, S. foeda, S. forreri, S. latissima, S. magnifica, S. tarda, S. montezuma, S. moricoides, S. roosevelti, S. spinimana and S. tenebrosa (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Strotheria gypsophila (Asteracea; ^{Villarreal-Quintanilla et al., 2017}). Synthlipsis densiflora (Brassicaceae; ^{Villarreal-Quintanilla et al., 2017}). Tarpela corpulenta, T. durangoensis and T. hoegei (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Telabis brevicollis (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Tetraclea subinclusa (Verbenaceae; ^{Villarreal-Quintanilla et al., 2017}). Thamnosma pailense and T. stanfordii (Rutaceae; ^{Villarreal-Quintanilla et al., 2017}). Thelocactus bicolor bolaensis, T. lausseri, T. macdowellii, T. rinconensis subsp. nidulans, Thelocactus rinconensis subsp. phymatothele and T. rinconensis subsp. rinconensis (Cactaceae; ^{González-Elizondo et al., 2017b}; ^{Villarreal-Quintanilla et al., 2017}). Thelesperma scabridulum (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Thelypodiopsis incisa (Brassicaceae; ^{Villarreal-Quintanilla et al., 2017}). Thelypodium longipes (Brassicaceae; ^{Villarreal-Quintanilla et al., 2017}). Tidestromia rhizomatosa and T. tenella (Amaranthaceae; ^{Villarreal-Quintanilla et al., 2017}). Tillandsia durangensis (Bromeliaceae; ^{González-Elizondo et al., 2017a}). Tiquilia tuberculata (Boraginaceae; ^{Villarreal-Quintanilla et al., 2017}). Thymophylla gentryi guatimape and T. gypsophila (Asteraceae; ^{González-Elizondo et al., 2017a}; ^{Villarreal-Quintanilla et al., 2017}). Tradescantia gypsophila (Commelinaceae; ^{Villarreal-Quintanilla et al., 2017}). Turbinicarpus beguinii subsp. pailanus, T. mandragora and T. subterraneus (Cactaceae; ^{Villarreal-Quintanilla et al., 2017}). Varilla mexicana var. gypsophila (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Villarrealia calcicola (Apiaceae; ^{Villarreal-Quintanilla et al., 2017}). Xanthisma pseudorestiforme (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Uma paraphygas (Phrynosomatidae; ^{Lavín et al., 2007}; ^{Lazcano et al., 2019}; ^{Ocampo Salinas et al., 2019}). Xylothamia pseudobaccharis, X. purpusii, X. riskindii and X. truncata (Asteraceae; ^{Villarreal-Quintanilla et al., 2017}). Xylotrechus durangoensis (Cerambycidae; ^{Noguera & Chemsak, 1996}). Yucca endlichiana, Y. linearifolia and Y. rigida (Asparagaceae; ^{Villarreal-Quintanilla et al., 2017}).

Mexican Plateau subprovince, stat. nov.

Austrocentral province ^{Smith, 1941: 99}.

Mesa Central region ^{West, 1964: 368}.

Plateau province ^{Ferrusquía-Villafranca, 1990: map (in part)} .

Zacatecan province ^{Ramírez-Pulido and Castro-Campillo, 1990: map (in part)} .

Southern Plateau (Zacatecan-Potosian) province ^{Arriaga et al., 1997: 62}.

Chihuahua Desert, S province ^{Escalante et al., 1998: 284}.

Zacatecan subregion ^{Hafner and Riddle, 2005: 227}; ^{Riddle and Hafner, 2006: 438}; ^{Neiswenter et al., 2019: 1848}.

Southern Plateau (Zacatecas-Mezquital Aridlands) province ^{Espinosa-Organista et al., 2008: 60}.

Zacatecan district ^{Morrone, 2019: 28}.

Mexican Plateau region ^{Sosa et al., 2018: 524}.

Southern Chihuahuan Desert area ^{Ocampo Salinas et al., 2019: 15}.

Mexican Plateau area ^{Vázquez-Cruz and Sosa, 2019: 446}.

Definition. It corresponds to the southernmost part of the Chihuahuan Desert province and includes the Saladan, Mexican Southern Arid and Tehuacán-Cuicatlán districts (Fig. 1).

Endemic taxa. Acourtia elizabethiae, A. moctezumae, A. oxylepis and A. venturae (Asteraceae; ^{De-Nova et al., 2018}). Agave garciae-mendozae (Asparagaceae; ^{De-Nova et al., 2018}). Agapema dentifasciata (Saturnidae; ^{Balcázar-Lara & Beutelspacher-Baigts, 2000a}; ^{Conabio, 2020}). Ageratina brandegeana (Asteraceae; ^{De-Nova et al., 2018}). Anisota punctata (Saturnidae; ^{Balcázar-Lara & Beutelspacher-Baigts, 2000a}; ^{Conabio, 2020}). Antiphytum parryi (Boraginaceae; ^{Lira-Charco et al., 2012}). Aristolochia nana (Aristolochiaceae; ^{De-Nova et al., 2018}). Brongniartia parryi (Fabaceae; ^{De-Nova et al., 2018}). Buxus moctezumae (Buxaceae; ^{De-Nova et al., 2018}). Carex evadens (Cyperaceae; ^{De-Nova et al., 2018}). Chomelia pringlei (Rubiaceae; ^{De-Nova et al., 2018}). Cienfuegosia intermedia (Malvaceae; ^{De-Nova et al., 2018}). Commelina queretarensis (Commelinaceae; ^{De-Nova et al., 2018}). Coreopsis guanajuatensis and C. queretarensis (Asteraceae; ^{De-Nova et al., 2018}). Coryphantha erecta, C. glassii and C. jalpanensis (Cactaceae; ^{De-Nova et al., 2018}). Cosmos atrosanguineus (Asteraceae; ^{De-Nova et al., 2018}). Cotinus carranzae (Anacardiaceae; ^{De-Nova et al., 2018}). Cucurbita pedatifolia (Cucurbitaceae; Lira & Rodríguez, 1999). Dahlia linearis and D. moorei (Asteraceae; ^{De-Nova et al., 2018}). Dalea polycephala (Fabaceae; ^{De-Nova et al., 2018}). Desmodium sericocarpum and D. subspicatum (Fabaceae; ^{De-Nova et al., 2018}). Echeveria humilis, E. lutea and E. palmeri (Crassulaceae; ^{De-Nova et al., 2018}). Echinocereus schmollii (Cactaceae; ^{De-Nova et al., 2018}). Erigeron subacaulis (Asteraceae; ^{De-Nova et al., 2018}). Grindelia robinsonii (Asteraceae; ^{De-Nova et al., 2018}). Gyrandra pterocaulis (Daphniphyllaceae; ^{De-Nova et al., 2018}). Habranthus mexicanus (Amaryllidaceae; ^{De-Nova et al., 2018}). Halimolobos multiracemosus (Brassicaceae; ^{De-Nova et al., 2018}). Hechtia pretiosa and H. zamudioi (Bromeliaceae; ^{De-Nova et al., 2018}). Heliopsis longipes (Asteraceae; ^{Zamudio & Galván Villanueva, 2011}). Hemiphylacus alatostylus (Asparagaceae; ^{De-Nova et al., 2018}). Hibiscus elegans (Malvaceae; Frixell, 1993). Kyrsteniopsis cymulifera (Asteraceae; ^{De-Nova et al., 2018}). Mammillaria lloydii, M. nana and M. perbella (Cactaceae; ^{Zamudio & Galván Villanueva, 2011}; ^{De-Nova et al., 2018}; ^{Conabio, 2020}). Morkillia mexicana (Zygophyllaceae; ^{Medina-Lemos, 2012}). Neobuxbaumia polylopha (Cactaceae; ^{De-Nova et al., 2018}). Neonesomia johnstonii (Asteraceae; ^{De-Nova et al., 2018}). Oldenlandia pringlei (Rubiaceae; ^{De-Nova et al., 2018}). Opuntia orbiculata, O. pilifera, O. rosea and O. streptacantha (Cactaceae; ^{Arias et al., 1997}; ^{De-Nova et al., 2018}). Pachyphytum kimnachii (Crassulaceae; ^{De-Nova et al., 2018}). Paradirphia boudinoti (Saturnidae; ^{Balcázar-Lara & Beutelspacher-Baigts, 2000a}; ^{Conabio, 2020}). Persea purpusii (Lauraceae; ^{De-Nova et al., 2018}). Phaseolus gladiolatus (Fabaceae; ^{De-Nova et al., 2018}). Pinguicula martinezii (Lentibulariaceae; ^{De-Nova et al., 2018}). Pluchea mexicana (Asteraceae; ^{De-Nova et al., 2018}). Psychotria diegoae (Rubiaceae; ^{De-Nova et al., 2018}). Randia hidalgensis (Rubiaceae; ^{De-Nova et al., 2018}). Rhynchospora angosturensis (Cyperaceae; ^{De-Nova et al., 2018}). Salvia connivens (Lamiaceae; ^{De-Nova et al., 2018}). Sedum corynephyllum (Crassulaceae; ^{De-Nova et al., 2018}). Senecio alvarezensis (Asteraceae; ^{De-Nova et al., 2018}). Senegalia sororia (Fabaceae; ^{De-Nova et al., 2018}). Sohnsia filifolia (Poaceae; ^{De-Nova et al., 2018}). Stenandrium verticillatum (Acanthaceae; ^{Thomas, 1999}). Strombocactus disciformis (Cactaceae; ^{Zamudio & Galván Villanueva, 2011}; ^{Conabio, 2020}). Tagetes moorei and T. parryi (Asteraceae; ^{De-Nova et al., 2018}). Tigridia catarinensis (Iridaceae; ^{De-Nova et al., 2018}). Tillandsia suesilliae (Bromeliaceae; ^{De-Nova et al., 2018}). Tradescantia murilloae (Commelinaceae; ^{De-Nova et al., 2018}). Valeriana otomiana (Caprifoliaceae; ^{De-Nova et al., 2018}). Verbesina potosina (Asteraceae; ^{De-Nova et al., 2018}). Viguiera potosina (Asteraceae; ^{De-Nova et al., 2018}). Villadia acuta and V. patula (Crassulaceae; ^{De-Nova et al., 2018}). Zinnia guanajuatensis (Asteraceae; ^{De-Nova et al., 2018}).

Saladan district, stat. nov.

Saladan subprovince ^{Morafka, 1977: 200}; ^{Vázquez-Cruz and Sosa, 2016: 1698}; ^{Díaz-Cárdenas et al., 2019: 864}; ^{Myers et al., 2019: 211}.

Chihuahuan Xeric Scrub ecoregion ^{Dinerstein et al., 1995: 104 (in part)}.

Zacatecan subregion ^{Hafner and Riddle, 2005: 227}.

North American Hot Deserts ecoregion ^{Challenger and Soberón, 2008: 103 (in part)}.

Saladan region ^{Scheinvar et al., 2017: 324}.

Definition. The Saladan district corresponds to southern Coahuila, southeastern Durango, Zacatecas, central northern San Luis Potosí, eastern Jalisco, and Aguascalientes (^{Morafka, 1977}; ^{Díaz-Cárdenas et al., 2019}).

Endemic taxa. Acourtia potosina (Asteraceae; ^{De-Nova et al., 2018}). Agathirsia testacea (Braconidae; ^{Wharton & Mercado, 2000}; ^{Conabio, 2020}). Ageratina oppositifolia and A. rhodopoda (Asteraceae; ^{De-Nova et al., 2018}). Alethia longipennis (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Allium fantasmasense and A. potosiense (Amaryllidaceae; ^{De-Nova et al., 2018}). Apodanthera cucurbitoides (Cucurbitaceae; ^{De-Nova et al., 2018}). Araeoschizus problematicus (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Argythamnia argentea (Euphorbiaceae; ^{De-Nova et al., 2018}). Ariocarpus bravoanus subsp. hintonii (Cactaceae; ^{De-Nova et al., 2018}). Aristolochia nana (Aristolochiaceae ^{De-Nova et al., 2018}). Astragalus racemosus and A. tioides (Fabaceae; ^{De-Nova et al., 2018}). Ateleia chiangii (Fabaceae; ^{De-Nova et al., 2018}). Atriplex reptans and A. valdesii (Amaranthaceae; ^{Estrada-Castillón et al., 2010}; ^{De-Nova et al., 2018}). Bouchetia procumbens (Solanaceae; ^{De-Nova et al., 2018}). Bouteloua chasei (Poaceae; ^{Estrada-Castillón et al., 2010}). Carex fuscolutea (Cyperaceae; ^{De-Nova et al., 2018}). Carphochaete schaffneri (Asteraceae; ^{De-Nova et al., 2018}). Castilleja galehintoniae and C. nitricola (Orobanchaceae; ^{Estrada-Castillón et al., 2010}; ^{De-Nova et al., 2018}). Ceratozamia zaragozae (Zamiaceae; ^{De-Nova et al., 2018}). Chaetodipus lineatus (Heteromyidae; ^{Best, 1993}; ^{Vázquez, 2017}). Cinnamomum bractifoliaceum (Lauraceae; ^{De-Nova et al., 2018}). Cirsium excelsius (Asteraceae; ^{De-Nova et al., 2018}). Clinopodium micromerioides (Lamiaceae; ^{De-Nova et al., 2018}). Crassomicrodus fulvescens (Braconidae; ^{Wharton & Mercado, 2000}; ^{Conabio, 2020}). Cynomys mexicanus (Sciuridae; ^{Treviño-Villarreal & Grant, 1998}; ^{Álvarez-Castañeda et al., 2019}). Dahlia spectabilis (Asteraceae; ^{De-Nova et al., 2018}). Dasylirion treleasei (Asparagaceae; ^{De-Nova et al., 2018}). Echeveria angustifolia (Crassulaceae; ^{De-Nova et al., 2018}). Eleodes montana (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Erigeron heteromorphus (Asteraceae; ^{De-Nova et al., 2018}). Euphorbia tomentella (Euphorbiaceae; ^{De-Nova et al., 2018}). Exhalimolobos parryi (Brassicaceae; ^{De-Nova et al., 2018}). Frankenia gypsophila and F. margaritae (Frankeniaceae; ^{Estrada-Castillón et al., 2010}). Gonolobus bifidus (Apocynaceae; ^{De-Nova et al., 2018}). Haplidus parvulus (Cerambycidae; ^{Noguera & Chemsak, 1996}). Hechtia capituligera (Bromeliaceae; ^{De-Nova et al., 2018}). Hemihyalea ludwigi (Arctiidae; ^{Balcázar-Lara & Beutelspacher-Baigts, 2000b}). Hemirrhagus elliotti (^{Jiménez, 1996}; ^{Mendoza, 2014}; ^{Conabio, 2020}). Hesperaloe chiangii (Asparagaceae; ^{De-Nova et al., 2018}). Ipomoea schaffneri (Convolvulaceae; ^{De-Nova et al., 2018}). Isocoma gypsophila (Asteraceae; ^{Estrada-Castillón et al., 2010}). Leiobunum mesopunctatum and L. royali (Sclerosomatidae; ^{Kury & Cokendolpher, 2000}; ^{Conabio, 2020}). Leucophyllum flyrii (Scrophulariaceae; ^{De-Nova et al., 2018}). Lophophora diffusa subsp. viridescens (Cactaceae; ^{De-Nova et al., 2018}). Lycianthes luisana (Solanaceae; ^{De-Nova et al., 2018}). Machaeranthera heterophylla (Asteraceae; ^{Estrada-Castillón et al., 2010}). Mammillaria bocasana subsp. eschauzieri and M. crinita subsp. leucantha (Cactaceae; ^{De-Nova et al., 2018}). Milla potosina (Asparagaceae; ^{De-Nova et al., 2018}). Moneilema opuntiae (Cerambycidae; ^{Noguera & Chemsak, 1996}). Muhlenbergia spatha (Poaceae; ^{De-Nova et al., 2018}). Nama rzedowskii (Boraginaceae; ^{De-Nova et al., 2018}). Nemastylis tenuis var. purpusii (Iridaceae; ^{De-Nova et al., 2018}). Nolina humilis (Asparagaceae; ^{De-Nova et al., 2018}). Parachrysina borealis (Melolonthidae; ^{Morón, 1996}; ^{Conabio, 2020}). Pellaea ribae (Pteridaceae; ^{De-Nova et al., 2018}). Penstemon potosinus (Plantaginaceae; ^{De-Nova et al., 2018}). Phemeranthus mexicanus (Montiaceae; ^{De-Nova et al., 2018}). Physalis cinerea (Solanaceae; ^{De-Nova et al., 2018}). Pinguicula debbertiana, P. gypsicola and P. takakii (Lentibulariaceae; ^{De-Nova et al., 2018}). Plectreurys zacateca (Scolopendridae; ^{Cupul-Magaña, 2020}; ^{Conabio, 2020}). Polygala brachyanthema and P. phoenicistes (Polygalaceae; ^{De-Nova et al., 2018}). Prionosciadium palmeri (Apiaceae; ^{De-Nova et al., 2018}). Rhodosciadium argutum (Apiaceae; ^{De-Nova et al., 2018}). Salvia schaffneri, S. lentiginosa and S. serpyllifolia (Lamiaceae; ^{De-Nova et al., 2018}). Sartwellia mexicana (Asteraceae; ^{Estrada-Castillón et al., 2010}). Sedum furfuraceum and S. potosinum (Crassulaceae; ^{De-Nova et al., 2018}). Senecio heterodontus (Asteraceae; ^{De-Nova et al., 2018}). Sisyrinchium zamudioi (Iridaceae; ^{De-Nova et al., 2018}). Scolopendra pachygnatha (Scolopendridae; ^{Cupul-Magaña, 2020}; ^{Conabio, 2020}). Sphinx pitzahuac (Sphingidae; ^{Conabio, 2020}; ^{León-Cortéz, 2000}). Stachys sandersii (Lamiaceae; ^{De-Nova et al., 2018}). Stenomorpha lata, S. lugubris, S. rufipes, S. sphaericollis and S. zacatecensis (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Strotheria gypsophila (Asteraceae; ^{Estrada-Castillón et al., 2010}). Tarpela subparallela (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Thelesperma scabridulum (Asteraceae; ^{Estrada-Castillón et al., 2010}). Thelocactus conothelos subsp. flavus and T. panarottoanus (Cactaceae; ^{De-Nova et al., 2018}). Tigridia potosina (Iridaceae; ^{De-Nova et al., 2018}). Tridax candidissima (Asteraceae; ^{De-Nova et al., 2018}). Turbinicarpus saueri subsp. knuthianus, T. schmiedickeanus subsp. andersonii, T. schmiedickeanus subsp. flaviflorus, T. schmiedickeanus subsp. klinkerianus, T. schmiedickeanus subsp. rioverdensis, T. schmiedickeanus subsp. rubriflorus, T. schmiedickeanus subsp. schwarzii and T. viereckii (Cactaceae; ^{De-Nova et al., 2018}). Verbesina hypoleuca and V. sororia (Asteraceae; ^{De-Nova et al., 2018}). Villadia cucullata (Crassulaceae; ^{De-Nova et al., 2018}). Vipio moneilemae (Braconidae; ^{Wharton & Mercado, 2000}; ^{Conabio, 2020}). Zaluzania mollissima (Asteraceae; ^{De-Nova et al., 2018}). Zephyranthes bella (Amaryllidaceae; ^{De-Nova et al., 2018}).

Mexican Southern Arid district

Mexican Southern Arid district ^{Cabrera and Willink, 1973: 37}.

Valley of Mezquital zone ^{Rzedowski, 1973: 64}.

Central Mexican Cactus Scrub ecoregion ^{Dinerstein et al., 1995: 104}.

Central Mexican Grasslands ecoregion ^{Dinerstein et al., 1995: 98}.

Central Mexican Mezquital ecoregion ^{Dinerstein et al., 1995: 104}.

Eastern Mexican Matorral ecoregion ^{Dinerstein et al., 1995: 104}.

Eastern Mexican Mezquital ecoregion ^{Dinerstein et al., 1995: 104}.

Mesa Central area ^{Pérez-Ponce de León, 2003: 126 (in part)}; ^{Domínguez-Domínguez and Pérez-Ponce de León, 2009: 836}.

Meridional Semiarid Highlands ecoregion ^{Challenger and Soberón, 2008: 103}.

Mesquital area ^{Vázquez-Cruz and Sosa, 2016: 1698}.

Definition. The Mexican Southern Arid district includes the areas known as Mesa Central and Mezquital Valley. ^{Rzedowski (1973)} considered this area to be floristically similar to the Chihuahuan desert. ^{Pérez-Ponce de León (2003)} examined the biotic affinities of the helminths parasitizing freshwater fish of this district, concluding that they were clearly Nearctic.

Endemic taxa. Acourtia venturae (Asteraceae; ^{Zamudio & Galván-Villanueva, 2011}). Alabagrus cora (Braconidae; ^{Wharton & Mercado, 2000}; ^{Conabio, 2020}). Anomiopsyllus perotensis (Ctenophthalmidae; ^{Acosta & Fernández, 2009}). Arracacia macvaughii (Apiaceae; ^{Zamudio & Galván Villanueva, 2011}). Astrophytum ornatum (Cactaceae; ^{Zamudio & Galván Villanueva, 2011}; ^{Conabio, 2020}). Baccharis zamoranensis (Asteraceae; ^{Zamudio & Galván Villanueva, 2011}). Beaucarnea compacta (Nolinaceae; ^{Zamudio & Galván Villanueva, 2011}). Bidens aequisquama var. guanajuatensis (Asteraceae; ^{Zamudio & Galván Villanueva, 2011}). Calibanus glassianus (Nolinaceae; ^{Zamudio & Galván Villanueva, 2011}). Carlowrightia venturae (Acanthaceae; ^{Zamudio & Galván Villanueva, 2011}). Chlorixanthe chapini and C. flavoviridis (Melolonthidae; ^{Morón, 1996}; ^{Conabio, 2020}). Chrysactinia luzmariae (Asteraceae; ^{Zamudio & Galván Villanueva, 2011}). Coryphantha erecta (Cactaceae; ^{Zamudio & Galván Villanueva, 2011}; ^{Conabio, 2020}). Citheronia splendens subsp. queretana (Saturnidae; ^{Balcázar-Lara & Beutelspacher-Baigts, 2000a}; ^{Conabio, 2020}). Cotinis orientalis (Melolonthidae; ^{Morón, 1996}; ^{Conabio, 2020}). Cratogeomys fulvescens (Geomyidae; ^{Hafner et al., 2005}; ^{Álvarez-Castañeda et al., 2017}). Echeveria calderoniae and E. xichuensis (Crassulaceae; ^{Zamudio & Galván Villanueva, 2011}; ^{Conabio, 2020}). Epicaerus costatus and E. durangoensis (Curculionidae; ^{Conabio, 2020}). Geraeus dugesi (Curculionidae; ^{Conabio, 2020}). Glandulicactus crassihamathus (Cactaceae; ^{Zamudio & Galván Villanueva, 2011}; ^{Conabio, 2020}). Hechtia pretiosa (Bromeliaceae; ^{Zamudio & Galván Villanueva, 2011}). Heliotropium queretaroanum (Boraginaceae; ^{Zamudio & Galván Villanueva, 2011}; ^{Conabio, 2020}). Ipomoea rzedowskii (Convolvulaceae; ^{Zamudio & Galván Villanueva, 2011}; ^{Conabio, 2020}). Mammillaria albiflora, M. duwei, M. herrerae, M. longimamma, M. multihamata, M. schwarzii and M. zeilmanniana (Cactaceae; ^{Zamudio & Galván Villanueva, 2011}; ^{Conabio, 2020}). Moneilema mexicanum (Cerambycidae; ^{Noguera & Chemsak, 1996}). Neotoma nelsoni (Cricetidae; ^{González-Ruiz et al., 2006}; ^{Fernández, 2012}; ^{Álvarez-Castañeda, 2018b}). Orizabus endrodianus (Melolonthidae; ^{Morón, 1996}; ^{Conabio, 2020}). Pachyphytum brevifolium, P. compactum and P. viride (Crassulaceae; ^{Zamudio & Galván Villanueva, 2011}; ^{Conabio, 2020}). Parachrysina mazatli (Melolonthidae; ^{Morón, 1996}; ^{Conabio, 2020}). Peromyscus bullatus (Cricetidae; ^{Hall & Dalquest, 1963}; González-Ruiz et al., 2005; ^{Álvarez-Castañeda, 2018c}). Phedius mexicanus and P. obovatus (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Polianthes multicolor (Asparagaceae; ^{Zamudio & Galván Villanueva, 2011}). Polypodium microgrammoides (Polypodiaceae; ^{Zamudio & Galván Villanueva, 2011}). Pomaria glandulosa (Fabaceae; ^{Zamudio & Galván Villanueva, 2011}; ^{Conabio, 2020}). Portulacca guanajuatensis (Portulacaeae; ^{Zamudio & Galván Villanueva, 2011}). Potentilla butandae (Rosaceae; ^{Zamudio & Galván Villanueva, 2011}). Priva ibugana (Verbenaceae; ^{Zamudio & Galván Villanueva, 2011}). Pseudobaris apicalis (Curculionidae; ^{Conabio, 2020}). Rubus macvaughianus (Rosaceae; ^{Zamudio & Galván Villanueva, 2011}). Sedum glassii, S. mocinianum and S. pacense (Crassulaceae; ^{Zamudio & Galván Villanueva, 2011}; ^{Conabio, 2020}). Senna guatemalensis var. hidalgensis (Fabaceae; ^{Zamudio & Galván Villanueva, 2011}; ^{Conabio, 2020}). Sideroxylon altamiranoi (Sapotaceae; ^{Zamudio & Galván Villanueva, 2011}). Sisyrinchium guanajuatense (Iridaceae; ^{Zamudio & Galván Villanueva, 2011}). Stachys turneri (Lamiaceae; ^{Zamudio & Galván Villanueva, 2011}). Stenomorpha umbrosa (Tenebrionidae; ^{Aalbu et al., 2002}; ^{Bousquet et al., 2018}; ^{Conabio, 2020}). Strepsylla queretana (Ctenophthalmidae; Acosta, 2010). Tetramerium carranzae (Acanthaceae; ^{Zamudio & Galván Villanueva, 2011}). Telegeusis hidalguensis (Coleoptera: Telegeusidae; ^{Zaragoza-Caballero, 2015}; ^{Conabio, 2020}). Thelocactus leucanthus (Cactaceae; ^{Zamudio & Galván Villanueva, 2011}; ^{Conabio, 2020}). Turbinicarpus alonsoi (Cactaceae; ^{Zamudio & Galván Villanueva, 2011}; ^{Conabio, 2020}). Verbesina suberosa (Asteraceae; ^{Zamudio & Galván Villanueva, 2011}). Xerospermophilus perotensis (Sciuridae; ^{Best & Ceballos, 1995}; ^{Fernández, 2012}; ^{Álvarez-Castañeda et al., 2016b}). Yucca queretaroensis (Asparagaceae; ^{Zamudio & Galván Villanueva, 2011}; ^{Conabio, 2020}). Zigadenus neglectus (Melianthaceae; ^{Zamudio & Galván Villanueva, 2011}). Zinnia acerosa var. guanajuatensis (Asteraceae; ^{Zamudio & Galván Villanueva, 2011}).

Tehuacán-Cuicatlán Valley district, reinst. name Tehuacán-Cuicatlán Valley zone ^{Rzedowski, 1973: 64}.

Tehuacán-Cuicatlán Valley province ^{Rzedowski, 1978: 107}; ^{Challenger, 1988: 647}; ^{Rzedowski and Reyna-Trujillo, 1990: map}; ^{Morrone, 2014: 32 (= Orizaba-Zempoaltepec district)}.

Pueblan Xeric Scrub ecoregion ^{Dinerstein et al., 1995: 104}.

Oriental Basin area ^{Fernández, 2012: 1431}: ^{Fernández et al., 2012: 560}.

Tehuacán Valley area ^{Vázquez-Cruz and Sosa, 2016: 1698}, ^{2019: 446}.

Tehuacán Valley region ^{Sosa et al., 2018: 524}.

Definition. The Tehuacán-Cuicatlán Valley district is situated in the states of Puebla and Oaxaca. It is characterized by many plant and animal endemic species (^{Rzedowski, 1978}; ^{Fernández, 2012}).

Endemic taxa. Acacia compacta (Fabaceae; ^{Rico & Rodríguez, 1998}). Afrida coagulata (Arctiidae; ^{Balcázar-Lara & Beutelspacher-Baigts, 2000b}). Agave macroacantha, A. titanota and A. triangularis (Asparagaceae; ^{García-Mendoza, 2011}). Antiphytum caespitosum and A. paniculatum (Boraginaceae; ^{Lira-Charco et al., 2012}). Apodanthera aspera (Cucurbitaceae; Lira & Rodríguez, 1999). Aristolochia teretifolia (Aristolochiaceae; ^{Kelly, 2000}). Asclepias cozanttii (Asclepiadaceae; ^{Juárez-Jaimes & Lozada, 2003}). Bakeridesia subcordata (Malvaceae; Frixell, 1993). Beaucarnea gracilis and B. purpusii (Nolinaceae; ^{Rivera-Lugo & Solano, 2012}). Blepharida schlectendalii and B. unami (Chrysomelidae; ^{Ordóñez-Reséndiz, 2014}; ^{Conabio, 2020}). Bouteloua reederorum (Poaceae; ^{Sandoval-Ortega, 2020}). Bursera pontiverteris (Burseraceae; Medina-Lemos, 2008). Buxus mexicana (Buxaceae; ^{Medina-Lemos, 2009}). Carlowrightia pringei (Acanthaceae; ^{Thomas, 1999}). Cephalocereus columna-trajani (Cactaceae; ^{Arias et al., 1997}, ²⁰¹¹). Citharexylum tetramerum (Verbenaceae; ^{Wilmann et al., 2000}). Coryphantha calipensis, C. pallida, C. picnacatha and C. pseudoradians (Cactaceae; ^{Arias et al., 1997}, ²⁰¹¹). Dasylirion lucidum and D. serratifolium (Nolinaceae; ^{Rivera-Lugo & Solano, 2012}). Dyschoriste purpusii (Acanthaceae; ^{Thomas, 1999}). Echinocactus platyacanthus (Cactaceae; ^{Arias et al., 1997}, ²⁰¹¹). Echinocereus pulchellus subsp. acanthosetus (Cactaceae; ^{Arias et al., 1997}, ²⁰¹¹). Euchaetes albaticosta (Arctiidae; ^{Balcázar-Lara & Beutelspacher-Baigts, 2000b}). Eudesmia quadrifasciata and E. tehuacana (Arctiidae; ^{Balcázar-Lara & Beutelspacher-Baigts, 2000b}). Ferocactus flavovirens, F. hemathacanthus, F. latispinus and F. recurvus subsp. recurvus (Cactaceae; ^{Arias et al., 1997}, ²⁰¹¹). Fouquieria purpusii (Fouquieriaceae; ^{Ezcurra & Medina, 1997}). Gossypium gossypioides (Malvaceae; Frixell, 1993). Golofa tepaneneca (Melolonthidae; ^{Morón, 1995}, ¹⁹⁹⁶; ^{Conabio, 2020}). Gymnolaena oaxacana (Asteraceae; ^{Villareal-Quintanilla, 2008}). Heliotropium axillare (Boraginaceae; ^{Lira-Charco et al., 2012}). Hemiphylacus mahindae (Hyacinthaceae; ^{Hernández, 1997}). Hibiscus longifuius (Malvaceae; Frixell, 1993). Holographis pueblensis and H. velutifolia (Acanthaceae; ^{Thomas, 1999}). Justicia cuicatlana, J. gonzalezii and J. pauciflia (Acanthaceae; ^{Thomas, 1999}). Lamourouxia smithii (Orobanchaceae; ^{Alvarado-Cárdenas, 2008}). Lemaireocereus hollianus (Cactaceae; ^{Arias et al., 1997}, ²⁰¹¹). Leucaena pueblana (Fabaceae; ^{Grether et al., 2006}). Mammillaria albilanata subsp. oaxacana, M. crucigera subsp. crucigera, M. crucigera subsp. tlalocci, M. discolor subsp. schmolli, M. haageana subsp. conspicua, M. haageana subsp. meissneri, M. hernandezii, M. huitzilopoctli subsp. huitzilopoctli, M. huitzilopoctli subsp. niduliformis, M. kraehenbuehlii, M. lanata, M. napina, M. oteroi, M. pectinifera, M. solicioides, M. sphacelata subsp. viperina, M. supertexta, M. tepexicensis and M. varieacuelata (Cactaceae; ^{Arias et al., 1997}, ²⁰¹¹). Marsdenia parvifolia (Asclepiadaceae; ^{Juárez-Jaimes & Lozada, 2003}). Mimosa purpusii (Fabaceae; ^{Grether et al., 2006}). Neobuxbaumia tetetzo and N. macrocephala (Cactaceae; ^{Arias et al., 1997}, ²⁰¹¹). Neortholomus scolopax (Lygaeidae; ^{Slater & Brailosvsky, 2000}; ^{Conabio, 2020}). Opuntia parviclada and O. tehuacana (Cactaceae; ^{Arias et al., 1997}, ²⁰¹¹). Pachycereus hollianus (Cactaceae; ^{Arias et al., 1997}, ²⁰¹¹). Parachrysina parapatrica (Melolonthidae; ^{Morón, 1996}; ^{Conabio, 2020}). Parasicyos dieterla (Cucurbitaceae; Lira & Rodríguez, 1999). Peromyscus mekisturus (Cricetidae; ^{Álvarez-Castañeda, 2018}a; ^{López-González et al., 2019}; ^{Castañeda-Rico et al., 2020}). Phaeosia lutea (Arctiidae; ^{Balcázar-Lara & Beutelspacher-Baigts, 2000b}). Phyllanthus subcuneatus (Phyllanthaceae; Martínez-Gordillo & Cervantes-Maldonado, 2008). Phymosia floribunda (Malvaceae; Frixell, 1993). Pinguicola mirandae (Lentibulariaceae; ^{Zamudio-Ruiz, 2006}). Polaskia chende and P. chichipe (Cactaceae; ^{Arias et al., 1997}, ²⁰¹¹). Pseudomitrocereus fulviceps (Cactaceae; ^{Arias et al., 1997}, ²⁰¹¹). Ptychoglene stenodora (Arctiidae; ^{Balcázar-Lara & Beutelspacher-Baigts, 2000b}). Schoenocaulon tenorioi (Melanthiaceae; ^{Frame et al., 2007}; ^{Torres-Colín & Delgado-Salinas, 2008}). Sibinia cuauhtemoc (Curculionidae; Clark, 1978). Sida pueblensis (Malvaceae; Frixell, 1993). Sidastrum tehuacanum (Malvaceae; Frixell, 1993). Styphnolobium burseroides (Fabaceae; ^{Téllez & Sousa, 1993}). Tehuacania howdeni (Melolonthidae; ^{Morón, 1996}; ^{Aragón et al., 2011}; ^{Conabio, 2020}). Yucca mixtecana (Asparagaceae; ^{García-Mendoza, 2011}). Zapoteca formosa subsp. mollicula (Fabaceae; ^{Andrade et al., 2012}).

Discussion

Several authors have shown that the biotic diversification of North American warm deserts has been the result of a complex history, with a substantial contribution of vicariance events (^{Gámez et al., 2017}; ^{Hafner & Riddle, 2005}; ^{Morafka et al., 1992}; ^{Riddle & Hafner, 2006}). If vicariance also contributed to the biotic history within the Chihuahuan Desert, the recognition of smaller, nested units within it is a prerequisite for a cladistic biogeographic analysis that may help understand its biotic history. Notably, ^{Scheinvar et al. (2017)} hypothesized that the divergence of northern and southern haplogroups of Agave lechuguilla (Asparagaceae) were consistent with the division of the Chihuahuan Desert into 2 subprovinces and hypothesized that this divergence could be related to ancient geomorphological and climatic events associated with the secondary uplift of North America over the Neogene. A similar divergence between species of Lindleya (Rosaceae) distributed in the subprovinces was detected by ^{Vázquez-Cruz and Sosa (2016)}. ^{Díaz-Cárdenas et al. (2019)} analyzed the species of Sceloporus (Squamata: Phrynosomatidae) from the Mapimian district, estimating that S. cyanostictus and S. gadsdeni may have diverged 1.48 m.y.a, when a large lake could have acted as a barrier leading to allopatrid speciation.

The Chihuahuan Desert province and its districts are hypothesized herein to represent natural biotic units, each harboring a characteristic assemblage of endemic taxa. Further data that could falsify these hypotheses are distributions of taxa restricted to some of these districts and excluding another. For example, finding that the 4 northernmost districts of the Chihuahuan Desert province have a set of endemic species that are not present in the Tehuacán-Cuicatlán Valley district may support the alternative hypothesis of recognizing a separate province (or subprovince) for the latter. These alternative hypotheses could be falsified undertaking a cladistic biogeographic analysis, based on the phylogenetic hypotheses of plant and animal taxa endemic to the area.

^{Muldavin (2002)} contrasted the recognition of biogeographic and ecological units but considered more appropriate to bring both approaches together. In this sense, we think that our approach is similar, as biogeographic regionalizations should be based on the recognition of areas of endemism, but at the same time the vegetation should be considered as another aspect to be incorporated in the recognition of natural biogeographic units (^{Morrone et al., 2017}). This integrative approach is more likely to produce a sound and useful regionalization.