Diversity of Flowering Plants in the Caatinga: an Analysis of Floristic and Phytosociological Studies

Abstract The Caatinga harbors the largest continuous expanse of Seasonally Dry Tropical Forests and Woodlands (SDTFW) in South America, characterized by a highly diverse flora and a significant number of endemic species. In this study, we compiled data on species distribution within the Caatinga by gathering information from 112 peer-reviewed floristic and phytosociological studies published up to December 2020. We characterized this database by identifying woody and non-woody species, checking their International Union for Conservation of Nature (IUCN) Red List status, highlighting the families represented by most species, and analyzing species distribution across Neotropical biomes, biogeographical districts, and Holdridge life zones. Our database includes 1,775 taxa identified at the species level (conservative richness), while the total estimated richness was 2,978 species, including unidentified specimens. However, our analysis revealed that the proportion of unidentified taxa in Caatinga studies decreased from 27.10% in 1985 to 12.31% in 2020. Of the conservative richness estimate, the non-woody component accounts for 48% (852 species) of species richness, while the woody component represents 52% (923 species). Fabaceae is the richest family, with 346 species, a common pattern in Neotropical dry forests. The genera Croton (35 species) and Ipomoea (30 species) were the most species rich. In total, we recorded 218 endemic species of the Caatinga, including 101 species specialized in SDTFW, as well as 1,456 native species considered non-specialized, meaning they are shared between Caatinga vegetation and savannas, non-semiarid seasonal forests, or tropical forests. Most species (1,321) have not yet been assessed by the IUCN Red List, while 37 species are classified as threatened. We observed that 70% of floristic and phytosociological surveys were conducted on crystalline terrains and that transition life zones play a crucial role in maintaining plant communities. Regional studies that provide species lists along with conservation status information are essential for informing local policies aimed at mitigating biodiversity loss and promoting the conservation of endemic and threatened species in the Caatinga.