Toward a comprehensive phylogeny of North American bladderworts (Utricularia, Lentibulariaceae)

Carnivorous plants in the genus Utricularia (bladderwort) are diverse and widespread, represented in North America primarily by free-floating aquatic species. In the Nearctic ecoregion, roughly corresponding to temperate North America, there are 20 species of Utricularia, comprising a small fraction of the approximately 270 species in the genus worldwide. However, despite their low number, the Nearctic species represent seven of the 18 taxonomic sections of Utricularia, a pattern that potentially reflects multiple ancestral dispersal events into North America. Most of the Nearctic bladderwort species are represented by DNA sequence data, yet there is no single genetic locus that has been sequenced for all species, and this has precluded a thorough evaluation of their phylogenetic relationships. In this study, we obtained DNA sequence data for genetic loci and species that had not been sequenced previously, to produce a fully sampled molecular phylogeny. The resulting phylogeny includes all species that occur in the USA and data from five DNA regions: one nuclear locus (internal transcribed spacer, ITS) and four plastid loci (trnK/matK, rpl20-rps12, rps16, and trnL-trnF). We recovered a close relationship between U. inflata and U. radiata, two species that both have aerenchymatous floral support structures, and which previously had not been sequenced for any of the same genetic loci. We also sequenced numerous U. macrorhiza individuals, and our data support the phylogenetic distinctness and molecular diagnosability of this species against U. australis, U. tenuicaulis, and U. vulgaris. Curiously, we discovered plants in Ohio, USA that were identified as U. tenuicaulis and U. × neglecta (= U. tenuicaulis × U. vulgaris), and these represent the first evidence of such plants being naturalized in North America. These previously overlooked species and hybrids highlight the importance of using DNA in plant surveys and the value of having a robust reference library of DNA sequences.