Phylogeny, biogeography, and character evolution of the genus Sophora s.l. (Fabaceae, Papilionoideae)

The papilionoid legume genus Sophora (Fabaceae) exhibits a worldwide distribution, but a phylogenetic framework to understand the evolution of this group is lacking to date. Previous studies have demonstrated that Sophora is not monophyletic and might include Ammodendron, Ammothamnus, and Echinosophora, but the relationships among these four genera (defined as Sophora s.l.) are unclear. Here we used a nuclear DNA dataset (ETS, ITS, SQD1) and a plastid DNA dataset (matK, rbcL, rpl32-trnL, trnL-F) of 654 accession sequences to reconstruct the phylogenetic relationships, estimate the divergence times and ancestral range of Sophora s.l., and infer the evolution of chromosome number and morphological characteristics. Our major aim was to reconstruct phylogenetic relationships to test monophyly and elucidate relationships within the genus. Our results indicated that Ammodendron, Ammothamnus, and Echinosophora are embedded within Sophora s.s. and that nine wellsupported clades can be recognized within comprise Sophora s.l. Ancestral character state estimation revealed that the most recent common ancestor of Sophora s.l. was a deciduous shrub that lacks rhizome spines and has unwinged legumes. Divergence times estimation and ancestral area reconstruction showed that Sophora s.l. originated in Central Asia and/or adjacent Southeast China in the early Oligocene (ca. 31 Mya) and dispersed from these regions into East and South Asia's adjacent areas and North America via the Bering land bridge. The analyses also supported a South American origin for S. sect. Edwardsia, which experienced rapid radiation with its major lineages diversifying over a relatively narrow timescale (8 Mya).

Automated summary

This study reconstructed the evolutionary relationships of the papilionoid legume genus Sophora using nuclear and plastid DNA datasets. It revealed that Sophora s.l. includes Ammodendron, Ammothamnus, and Echinosophora, and can be further divided into nine well-supported clades. Ancestral character state estimation showed that the most recent common ancestor of Sophora s.l. was a deciduous shrub with unwinged legumes. Divergence times estimation and ancestral area reconstruction suggested that Sophora s.l. originated in Central Asia and/or adjacent Southeast China and dispersed to other regions.