Vallisneria (Hydrocharitaceae): novel species, taxonomic revisions, and hybridization

Vallisneria is a cosmopolitan genus of aquatic plants comprising 14 species within the family Hydrocharitaceae. Previous research suggests Vallisneria is a more speciose genus than current taxonomy indicates, and there remains contention on the level of species diversity within the genus. In order to address some of these taxonomic issues, this study estimates phylogenetic relationships within the genus using a previously published molecular dataset augmented with previously unsampled species through the use of maximum likelihood analyses for all molecular data partitions (e.g., nrITS, cpDNA, and combined nuclear and cpDNA datasets). Based on our findings, we recommend the resurrection of two Vallisneria species (V. gracilis and V. neotropicalis), and formally recognize and describe a new species (V. jacobsii). Morphological data was shown to be useful for some species delimitation but overall, molecular sequence data provided the best estimates of species identification for cultivated specimens. We also show the presence of naturally occurring putative Vallisneria hybrids within Northern Territory, Australia, and give conclusive evidence that non-native hybrids are being used for a restoration project in Crystal River, Florida.