Phylogeny of Sparganium (Typhaceae) revisited: non-monophyletic nature of S. emersum sensu lato and resurrection of S. acaule

Abstract

The diploid aquatic genus Sparganium (Typhaceae) comprises ca. 14 species mainly in cool temperate regions of the world. Among these, S. emersum comprises two infraspecific taxa, subspecies acaule from eastern North America and subspecies emersum from Eurasia and western North America (and occasionally from eastern North America as well). However, there has been some discussion regarding the monophyly of S. emersum sensu lato. We tested the hypothesis of a polyphyletic S. emersum sensu lato in a phylogenetic framework. Sequence data from six plastid DNA regions and nuclear phyC were analyzed using maximum parsimony, maximum likelihood, and Bayesian inference. We obtained a moderately resolved phylogeny with the plastid DNA data set, while phylogenetically less-informative phyC was useful to distinguish morphological species and discern hybrid and non-hybrid specimens. Sparganium emersum sensu lato was resolved as polyphyletic, clustering with S. angustifolium and S. glomeratum, respectively. Sparganium acaule is resurrected to be a sister to S. glomeratum, for which synapomorphic and distinguishing morphological characters are provided. Three cases of hybridization were detected.