Diversity of Cactaceae in the Flora of Bajío and adjacent regions (Mexico)

Background: Recent floristic lists indicate that the Mexican Bajío is a diverse area in terms of the number of species and endemism of Cactaceae. Questions and/or Hypotheses: 1) How many taxa are distributed in the Bajío and adjacent regions? 2) What are the vegetation types and biogeographic provinces with the greatest species richness? 3) What are the areas with the highest level of endemism? Studied species: Cactaceae family. Study site and dates: Bajío region (Guanajuato, Querétaro and northern part of Michoacán), México, which was visited between 2014 and 2022. Methods: With the use of herbarium, field collections and iNaturalist/iNaturalistMX records, a database was constructed from which species richness, weighted endemism and weighted endemism corrected by one-third degree cells were estimated. Results: Thirty genera and 125 species of cacti are reported. Xerophilous scrub is the type of vegetation that hosts the greatest number of species. The Chihuahuan Desert is the province with the highest level of richness. The cells with the highest richness and weighted endemism are found between the provinces of the Chihuahuan Desert and the Sierra Madre Oriental. In contrast, there is a decrease toward the Trans-Mexican Volcanic Belt. Conclusions: Of the three biogeographic provinces that converge in the Bajío region —the Trans-Mexican Volcanic Belt, the Chihuahuan Desert, and the Sierra Madre Oriental— the largest number of endemic species is found on the borders between the latter two, likely because this region was a climatic refuge during the Pleistocene.