A RADseq phylogeny of Barleria (Acanthaceae) resolves fine-scale relationships

Barleria is a genus of approximately 300 species of herbs, shrubs or, rarely, trees, that is broadly distributed across the Paleotropics. The genus is especially diverse in Tanzania, Angola, and Madagascar. A recent molecular study sampled 53 Barleria species and gathered data for five molecular markers (i.e., four chloroplast loci and the nuclear nrITS) to find support for the recognition of two subgenera previously circumscribed based on morphology, subg. Barleria and subg. Prionitis. That study further reconstructed four previously recognized sections (i.e., Fissimura, Prionitis, Somalia, Stellatohirta) as monophyletic, while three others (i.e., Barleria, Cavirostrata, Chrysothrix) were recovered as para- or polyphyletic. The present study aimed to reconstruct phylogenetic relationships within Barleria based on a broader sample of taxa and many more characters. We sampled 190 accessions representing 184 taxa, including varieties and subspecies. The dataset includes 167 of the ca. 300 species currently recognized or about 56% of total species diversity. We relied heavily on herbarium specimens to sample across the taxonomic breadth and geographic range of Barleria. Single nucleotide polymorphism data were generated using double-digest restriction-site associated DNA sequencing (ddRADseq). The maximum likelihood phylogeny corroborated the topology estimated from the chloroplast and nrITS data, but with greatly increased resolution and support for fine-scale relationships. A coalescent analysis failed to resolve distant evolutionary relationships across Barleria and between Barleria and outgroups, but recovered the same or similar topologies within each Barleria section. Importantly, the ddRADseq phylogeny recovered seven major lineages within subg. Barleria and resolved a polytomy that included B. cristata, the type species of the genus. The topology suggests at least four independent dispersal events to Madagascar followed by three subsequent radiations. Our results broadly inform our understanding of diversity and evolution in one of the largest genera of Acanthaceae, representing an important step towards a stable subgeneric classification for the genus.