| Summary: | Gypsum soils occur around the world, mainly in arid regions. These harsh environments promote unusual flora with high degrees of endemism. Mexico has extensive gypsum outcrops, but their flora has been poorly studied. However, the highest species richness and endemism are expected to be concentrated in Mexico’s northern dry regions. To promote the study of this flora and its conservation, we estimate how well sampled it is, quantify species richness, identify centers of endemism, and detect which gypsum outcrops lie within federal protected natural areas (PNA). We conducted exhaustive literature and herbaria reviews to generate a database of botanical records on gypsum soils. The total species and gypsophyte richness were calculated using cell grids. Centers of endemism were identified using the corrected weighted endemism index (CWE). We mapped the gypsum outcrops within PNA polygons. The most collected sites are Cuatro Ciénegas (Coahuila) and Santo Domingo Tonalá (Oaxaca), which also had the highest total species richness. Nevertheless, gypsophyte richness was higher in Cuatro Ciénegas and Nuevo León. The CWE identified seven gypsophyte centers of endemism. Mexico hosts the most diverse gypsophile flora in the world, despite having been only partially studied and collected. The regions with the highest species richness and endemism are unprotected.
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