A critical analysis of the Fragilaria vaucheriae complex (Bacillariophyta) in Europe

Abstract

<i>Fragilaria vaucheriae</i> is one of the most common <i>Fragilaria</i> species in Europe, typically reported from impacted, eutrophic water bodies. Despite its ubiquity, the species presents a broad morphological variability, urging a complete taxonomic revision based on the analysis of the morphology of a substantial number of historic and recent populations. In the present study, type material of <i>Exilaria vaucheriae</i>, <i>Fragilaria rinoi</i>, and<i> Echinella fasciculata </i>&beta; [var.] <i>truncata</i> was investigated using LM and SEM observations, together with more than 10 historic and recent populations. The results based on these comparisons show that <i>Fragilaria vaucheriae</i> is most likely a rather rare <i>Fragilaria</i> species in Europe and that most populations should be identified as <i>Fragilaria truncata</i>, a new combination made here based on <i>Echinella fasciculata </i>&beta; <i>truncata</i>. The observations made in this study also resulted in the description of several new species, often with distinct ecologies and distributions: <i>Fragilaria catenarinoi</i> Van de Vijver et D.M.Williams sp. nov., <i>F. kellyana</i> Van de Vijver, D.M.Williams et Ector sp. nov., <i>F. landnama</i> Van de Vijver et Iris Hansen sp. nov., <i>F. thingvellirensis</i> Van de Vijver et G.S.JĂłnsson sp. nov., <i>F. vandekerckhoveana</i> Van de Vijver sp. nov., <i>F. vaucheriaefalsa</i> Van de Vijver et D.M.Williams sp. nov. and <i>F. vaucheriaerobusta</i> Van de Vijver, C.E.Wetzel et Ector sp. nov. Important features to discriminate the different species include valve outline (linear versus lanceolate), the presence of 'shoulders' beyond the apices, the presence of striae (and the formation of colonies), the stria density and the shape and structure of the central area. Using an analysis of the associated diatom flora, the ecological preferences of each taxon are briefly discussed.