LAUSR

PREMISE Apomixis, asexual reproduction by seed, spore, or egg, has evolved repeatedly across the tree of life. Studies of animals and angiosperms show that apomictic lineages are often evolutionarily short-lived and frequently exhibit different distributions than their sexual relatives. However, apomixis is rare in these groups. Less is known about the role of apomixis in the evolution and biogeography of ferns, where ~10% of species are apomictic. Apomixis is especially common in the fern genus Pteris (34-39% of species), but due to the limited taxonomic and geographic sampling of previous studies, the true frequency of apomixis and its associations with geography and phylogeny in this lineage remain unclear. METHODS We used spore analyses of herbarium specimens to determine reproductive mode for 127 previously unsampled Pteris species. Then, we leveraged biogeographic and phylogenetic analyses to estimate the global distribution and evolution of apomixis in Pteris. KEY RESULTS Among all Pteris species examined, we found 21% to be exclusively apomictic, with 71% exclusively sexual and 8% having conflicting reports. Apomixis is unevenly distributed across the range of the genus, with the paleotropics exhibiting the highest frequency, and has evolved numerous times across the Pteris phylogeny, with predominantly East- and South-Asian clades containing the most apomictic species. CONCLUSIONS Apomixis arises frequently in Pteris, but apomictic species do not appear to diversify. Species that encompass both apomictic and sexual populations have wider ranges than exclusively sexual or apomictic species, suggesting sexual and apomictic ferns could occupy separate ecological niches. This article is protected by copyright. All rights reserved.