Taxonomic reappraisal of the freshwater brown algae Bodanella, Ectocarpus, Heribaudiella, and Pleurocladia (Phaeophyceae) on the basis of rbcL sequences and morphological characters

This study examines the phylogenetic relations among freshwater species of brown algae using RUBISCO large subunit (rbcL) sequences, in conjunction with diagnostic morphological and developmental traits. We focused on the phylogenetic and taxonomic placement of five freshwater species, Bodanella lauterborni, Ectocarpus siliculosus, Heribaudiella fluviatilis, Pleurocladia lacustris, and Porterinema fluviatile, each of which has traditionally been assigned to the Ectocarpales by most authors. These freshwater species were compared with 26 marine taxa of brown algae from nine orders, with particular emphasis on families within the Ectocarpales. Results of BLASTn searches and later phylogenetic analyses placed all freshwater taxa within the Phaeophyceae, but phylogenetic inferences do not support their traditional classifications at the ordinal level. There was no support for the inclusion of H. fluviatilis or B. lauterborni in the Ectocarpales, but instead formed a well-supported clade intermediate between the Syringodermatales and Sphacelariales. Although morphologies of these two species are relatively distinct and remain stable in culture, B. lauterborni nested between two populations of H. fluviatilis (on the basis of rbcL data) from British Columbia and Germany, making a reclassification of these two species necessary. Molecular and morphological data clearly place two other freshwater taxa, Pleurocladia lacustris and (freshwater) E. siliculosus in the Ectocarpales, each nesting among marine members of the Ectocarpaceae. When compared with sequences from 13 species from several families within the Ectocarpales, Pleurocladia is most closely related to members of the Ectocarpaceae and may be a sister taxon to the Scytosiphonaceae. DNA sequences from a freshwater isolate of E. siliculosus from Australia were nearly identical to those from a marine isolate from Germany. Molecular data did not resolve the ordinal status of a freshwater Porterinema fluviatile, but indicated that this species should not be classified within the Ectocarpales.