Plant species that grow only on unusual soils represent a significant proportion of plant diversity worldwide. These unique endemic communities are comprised of resilient and sometimes bizarre plants that thrive on difficult soils that most plant species cannot tolerate. One of the most widespread, yet understudied substrate-endemic floras of the world is that of gypsum soils. Gypsum (CaSO4·2H2O) soils occur worldwide in arid and semiarid ecosystems, posing serious restrictions to plant life. Despite these limitations, gypsum soils host rich endemic floras that have evolved independently on five continents. Plant communities growing on gypsum represent an excellent opportunity to investigate soils as a driving force in plant evolution and ecology, offering key insights into such fundamental biological processes as adaptation, the formation of new species, and the factors controlling plant community composition. Here we present the first global assessment of an edaphic endemic flora, providing information on the diversity, functional traits and conservation status of plants restricted to gypsum soils worldwide. Over 1200 taxa are restricted to gypsum in the world. These taxa belong to 86 families grouped in 32 orders, ranging from recently diversified groups like Poales to ferns, indicating restriction to gypsum soils evolved separately in different lineages of the plants tree of life and occurs in very distantly related groups. Most species are small perennial woody plants and almost half of the taxa are local endemics, pointing at the rarity and potential vulnerability of gypsophilic floras worldwide. Notably, more than a third of the gypsum endemic taxa have been listed in conservation reports or red lists and onefourth are under a certain degree of protection. Our study highlights the singularity of gypsum ecosystems globally and calls for urgent action to preserve these unique plant communities.

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