Phylogeny of Dyschoriste (Acanthaceae)

The pantropical and poorly known genus Dyschoriste Nees is closely related to Ruellia in the Acanthaceae. The present study included 38 accessions of 28 species as sources of DNA data for one nuclear (nrITS) and four chloroplast (psbA-trnH, trnS-trnG, ndhF-rpl32, rpl32-trnL(uag) intergenic spacers) regions to provide the first estimate of the phylogeny of the genus. We found that Dyschoriste is strongly supported as monophyletic inclusive of Apassalus Kobuski, Chaetacanthus Nees, and Sautiera Decne. Within Dyschoriste, three geographically cohesive lineages were recovered with moderate to strong support: a mainland African clade, a Caribbean and southeastern United States clade, and a South and Central America clade. A third New World clade composed of accessions from the south central through southwestern US to Mexico is weakly supported and corresponds to the D. linearis species complex recognized by previous researchers (six of the ten taxa putatively part of this complex were sampled). Surprisingly, the sympatric but morphologically distinct D. angustifolia is part of this clade. A second Old World clade unites taxa from across the Old World tropics (mainland Africa, Madagascar and southeast Asia). Some aspects of relationships among these main clades were unresolved or not strongly supported and two Old World taxa, south Asian D. dalzellii and the wide ranging D. nagchana were not placed with confidence in any of these clades. The simplest explanation for the current distribution of the genus is that there was a single dispersal event of Dyschoriste from the Old to the New World, with a subsequent radiation in the New World.