Areas of endemism (AEs) are fundamental entities of analysis in biogeography and a key step for biogeographical regionalization. Even though many studies have contributed to the biogeographical knowledge of southern USA flora, no endemicity analysis (EA) has been conducted that would include a large number of native seed plant species from different families. A new analysis of plant spatial patterns is important as a first step for a future updated floristic regionalization of North America North of Mexico. It has become easier to accomplish owing to the increased availability of large-scale digitized distributional data and statistical methods of biogeographic analysis. Here we identify the AEs in SC/SW USA using digitized plant specimen data available from IDigBio. We built a database with 81,851-specimen point records of 400 selected mostly angiosperm species and applied the NDM/VNDM method of endemicity analysis. We then compare the established 26 AEs in the area of study with the floristic provinces in two comparatively recent regionalization systems of USA. To understand the spatial patterns, we pay some attention to the information on relationships of the endemic species found in phylogenetic literature.

Digitized herbarium data were downloaded from the Integrated Digitized Biocollections (iDigBio accessed January –April 2020), cleaned to eliminate duplicates and other erroneous records, and contrasted with those documented by the Biota of North America Project (BONAP; https://bonap.org, accessed April–May 2020), online databases (EOL: https://eol.org/), and literature (Turner at al., 2003; FNA).