Phylogeny and biogeography of the genus Zornia (Leguminosae: Papilionoideae: Dalbergieae)

Abstract

AbstractThe genus Zornia has a pantropical distribution and comprises 80 species in two subgenera (Myriadena, Zornia) and three sections (Zornia, Isophylla, Anisophylla). The genus is characterized mainly by flowers arranged in a spiciform inflorescence, with paired peltate bracteoles protecting each flower, and stipules that resemble the bracteoles. Phylogenetically Zornia is a member of the informal Adesmia clade of the Dalbergioid group, being most closely related to the predominantly South American genera Poiretia and Amicia. Phylogenetic analyses of DNA sequence data from the internal transcribed spacer region of nuclear ribosomal DNA and the plastid trnL–trnF intron and spacer, including multiple accessions of species of all subgenera and sections, support the monophyly of Zornia and indicate that Poiretia is sister to Zornia. All traditional subgenera and sections of Zornia are resolved as para– or polyphyletic in our study. Nevertheless, two major clades can be recognized. Time–calibrated phylogenetic analyses suggest that most Zornia species diverged 8–10 Ma and reveal that only one migratory event occurred within the genus ca. 5 Ma from America to the Old World probably via long–distance dispersal.