Euphorbia villarrealii, a new species from harsh environments of Coahuila, Mexico

A new species of Euphorbia subg. Chamaesyce sect. Anisophyllum from harsh environments of Coahuila, Mexico, is described and illustrated with photos and a line drawing. This species was collected during a study in the Cuatro Ciénegas basin on gypsum and salty gypsum soils. Further research and collection studies revealed it as a new species, which is distinguished by the combination of an annual habit, glabrous herbage, entire leaves, entire-capitate styles, minute involucral appendages, and microscopically papillose white seeds. It is known only from three localities, and following IUCN Red List categories and criteria, we propose a preliminary assessment as Endangered (EN). Euphorbia villarrealii increases the known diversity of the section Anisophyllum within the Chihuahuan Desert, a primary center of diversity for the taxon. This species also increases the estimated endemicity in gypsum, salty and salty gypsum soils in the region.