The uneven global distribution of plant diversity remains a fundamental question in biogeography. Using dated phylogenies of over 300,000 plant species and ancestral biogeographical stochastic mapping, we show that in-situ speciation is the predominant process underlying extant plant diversity and accounts for 78 % of biogeographic events across realms. The Neotropic contributed 37 % of in-situ speciation, likely due to its role as center of species diversification. Dispersal between realms was less frequent (16 % of events) but facilitated floristic exchanges, especially in eastern Hemisphere. Extinction was least frequent but more pronounced in East Asia. These findings support the tropical conservatism hypothesis in which many clades originated in the tropics and only recently expanded into temperate zones, where limited time and biome conservatism have restricted speciation and diversity.

Funding provided by: Division of Environmental BiologyROR ID: https://ror.org/03g87he71Award Number: 2345994 Funding provided by: Division of Biological InfrastructureROR ID: https://ror.org/04qn9mx93Award Number: 2416314 Funding provided by: Alfred P. Sloan FoundationROR ID: https://ror.org/052csg198Award Number: Funding provided by: Stanford UniversityROR ID: https://ror.org/00f54p054Award Number: