East Asia-eastern North America disjunction revisited: Possible westward colonization route via the Western Palearctic in Carex sect. Paniceae (Cyperaceae)

Abstract

Carex sect. Paniceae sensu lato (s.l.) exhibits two major disjunct centers of diversity: eastern North America and East Asia. This pattern, commonly observed in other plant groups, has been associated with trans-Pacific dispersal from Asia to America and subsequent local extinctions in western North America. This study reconstructed a phylogenetic tree using two nuclear (external transcribed spacer and internal transcribed spacer) and three plastid (matK, trnL-F, and rpl32-trnLUAG) regions, along with 474 nuclear loci from high-throughput sequencing (Hyb-Seq). Dating analysis and ancestral area reconstruction were used to investigate the evolutionary and biogeographic history of sect. Paniceae s.l. A broader circumscription of sect. Paniceae s.l., incorporating sects. Bicolores and Laxiflorae, is established. Two primary clades were identified: one clade predominantly diversified in North America and the other in East Asia. Biogeographic analyses suggested a likely origin of sect. Paniceae s.l. in the Palearctic during the Late Miocene. The most probable scenario involved dispersal to eastern North America via the Western Palearctic, followed by subsequent dispersal into western North America, other parts of the continent, and back to the Old World. Within East Asia, the group was inferred to have diversified du