Nuclear phylogenomics of Eperua (Leguminosae) highlights the role of habitat and morphological lability in dispersal and diversification across Amazonia and in the Caatinga-Cerrado ecotone

Eperua is a genus of Neotropical trees that forms a major component of tropical lowland forests in Amazonia, especially in the Guiana Shield and on white-sand forests. One species occurs in the Cerrado-Caatinga ecotone, and the genus also inhabits riverine and terra firme forests. Species in Eperua exhibit one of two drastically different floral architectures and inflorescence types, each associated with distinct pollinators. Prior phylogenetic studies of Eperua have revealed an unstructured topology concerning floral architectures and inflorescence types. In addition, no investigation has been conducted on how the evolution of these traits and habitat preferences influenced the dispersal and diversification of Eperua. Using target capture sequencing, we inferred the most comprehensive phylogeny for Eperua to date, sampling all 19 known species, five for the first time. We used coalescence, concatenation, and network methods to infer the Eperua phylogeny and investigate sources of incongruence impacting resolution and support. We reconstructed the biogeographic history and ancestral states for the flower architecture, inflorescence type, and habitat preference. Our phylogenomic analyses successfully resolved relationships within Eperua, attributing conflicts between the species tree and concatenated tree to gene tree discordance linked to reticulation events. Biogeographical analyses indicate that Eperua originated and initially diversified in the white-sand forests of the Guiana Shield. A subsequent adaptation to riverine and terra firme forests enabled Eperua to expand into new habitats and regions. Still, its historical preference for white-sand forests probably accounts for its absence in the southern and western parts of Amazonia. Ancestral geographic areas and corolla morphotype reconstructions suggest that speciation in Eperua has occurred in sympatry, likely driven by pollinator shifts mediated by drastic changes in floral architecture.