Disentangling the phylogeny of bladderworts (Utricularia sect. Utricularia: Lentibulariaceae) based on plastid and nuclear data.

Abstract

Utricularia sect. Utricularia L. comprises fixed or free-floating aquatic macrophytes with very similar vegetative and floral traits which make their taxonomic identification a challenging task. Moreover, several lines of evidence, including pollen malformation, chromosome rearrangements and the sterility of some species have led to a hypothesis of interspecific hybridization. In this study, we present phylogenetic hypotheses for 21 of the 37 known species for the section Utricularia. We sequenced nuclear genes LEAFY and RPB2 and the plastid intergenic spacer rpl20-rps12. Furthermore, we used previously published plastidial data for rbcL and matK, beyond the nuclear ribosomal internal transcribed spacer (ITS) region, to perform phylogenies using Bayesian inference, maximum likelihood, parsimony and coalescent-based methods based on individual markers, partitioned and combined nuclear and plastid DNA. In addition, we propose phylogenetic networks, which we use to investigate hybridization events. Our nuclear and plastid gene trees are generally congruent but disagree in places that were punctually discussed. Discordance between the trees from different DNA markers can be due to incomplete lineage sorting or can indicate possible occurrence of reticulate evolution, and our findings may suggest hybridization. Molecular analysis demonstrated the occurrence of five main clades in section Utricularia (named clades A, B, C, D and E), and it was possible to infer evolutionary histories for some morphological characters. Our phylogenetic inferences imply that Utricularia sect. Utricularia as currently circumscribed is paraphyletic, and that Utricularia olivacea should be segregated into a separate section to maintain the monophyly of the section.