Morphological and molecular analyses of Vaucheria section Piloboloideae (Xanthophyceae: Vaucheriaceae) indicate alternative species identities for broadly distributed taxa

The discovery of a previously unrecorded Vaucheria species in subtidal marine habitats in Western Australia has led to a review of species included in Vaucheria section Piloboloideae, a taxon that includes several problematic invasive species. Molecular analyses placed this species in a clade including the New Zealand Vaucheria aestuarii and additionally indicated conspecificity with specimens from the North Sea that have been previously regarded as invasive V. longicaulis. However, our molecular analyses from the Californian type locality of V. longicaulis have shown that the North Sea taxon is not that species. Instead, it belongs to V. aestuarii, previously described from New Zealand, now also discovered by us at the coast of Western Australia. The sequences from the type locality of V. longicaulis, however, match those of an unidentified Vaucheria, coincidentally also found in the North Sea, reported as Vaucheria sp., and also recently referred to V. aff. compacta from Svalbard in the Arctic. Our work provides a taxonomic framework for two widespread invasive species and a key to all known species of the section Piloboloideae.