Phylogenomics of the tropical plant family Ochnaceae using targeted enrichment of nuclear genes and 250+ taxa

Abstract

Targeted capture of nuclear genes increasingly contributes to unravelling phylogenetic relationships that hitherto remained unresolved because of limitations of traditional Sanger sequencing. In particular, the study of tropical plant families has been compromised because they often rely on highly degraded DNA obtained from herbarium specimens. One such example is the pantropical Ochnaceae, which comprises 33 genera and approximately 550 species, occurring mostly in savannas and moist tropical forests. Here, we developed a set of baits covering about 660,000 bp from 275 nuclear genes used for the targeted enrichment based on all but one genus and more than 250 species. Using this novel dataset, we resolved the phylogenetic backbone of Ochnaceae, including that of Ochninae, and we established new relationships. Most importantly, our findings highlight that the neotropical and palaeotropical taxa of Sauvagesia form independent clades, requiring the re-erection of formerly separate genera. Ouratea and Ochna (both Ochninae), by far the most species-rich genera and represented by 120 and 41 species, respectively, came out as monophyletic. In contrast, the third-most species-rich genus, Campylospermum, is polyphyletic in two distinct clades. Ouratea, the only neotropical genus of Ochninae, was sister to the five palaeotropical genera of this subtribe. The bait kit developed in this study proved to be particularly useful for unravelling relationships within Ochninae, which includes about two-thirds of the species diversity in the family.