Phylogenetic Relationships among Old World Ruellia L.: A New Classification and Reinstatement of the Genus Dinteracanthus Schinz

Abstract

The genus Ruellia (Acanthaceae) consists of some ca. 350 species that are concentrated in tropical and subtropical regions of the world. Old World Ruellia have never been the focus of explicit phylogenetic study, yet comprise the earliest diverging lineages in the genus and contain upwards of 100 species. We sampled 52 accessions representing 29 OW species of Ruellia for phylogenetic analysis. Results yielded five clades that were strongly supported and marked by morphological synapomorphies. Analyses additionally recovered a newly recognized lineage within the tribe Ruellieae, a small radiation of plants in the deserts of Namibia and Angola, and the name Dinteracanthus is available for reinstatement. Divergence time analysis using a primary fossil calibration revealed relatively young estimates for crown ages of all five clades of OWRuellia (2.5 Ma - 630,000 ypb) as well as for Dinteracanthus (2.0 Ma). Ancestral state reconstruction of pollination systems among OW Ruellia suggest a minimum of two transitions from short-tongued insect pollination to nocturnal moth pollination, one from short-tongued insect to bird pollination, and one reversal from nocturnal moth pollination back to short-tongued insect pollination. We formally delimit the five clades of OW Ruellia as sections and present a key to aid in their identification: sect. Eusiphon, sect. Dipteracanthus, sect. Madagasikara, sect. Pseudoruellia, and sect. Discifolia. We provisionally treat 77 of 97 species of OW Ruellia among these five sections, with the remaining names considered to be unresolved.