Revision of European Brachysira species (Brachysiraceae, Bacillariophyta): I. The Brachysira microcephala - B. neoexilis enigma

ABSTRACT

The taxonomic identity of several similar Brachysira species in Europe is investigated based on a combination of the analysis of original type material, additional historic samples, and modern samples. Brachysira microcephala and B. neoexilis can be separated based on morphological and ecological differences. Brachysira microcephala shows a lanceolate valve outline lacking convex margins but with protracted, rostrate to non-protracted, acutely rounded apices. The species prefers oligotrophic, acidic conditions. Brachysira neoexilis possesses lanceolate valves with rounded, convex margins and distinctly protracted, capitate to subcapitate apices, and typically occurs in oligotrophic lakes and rivers with a pH ranging from slighty acid to cleary alkaline. In addition, the type materials of B. liliana and B. neglectissima, two species showing some morphological similarities with the other two species were reexamined. Both taxa have a high stria density, with individual striae not resolvable in LM and prefer calcium-bicarbonate, oligotrophic, alkaline lakes. All species are illustrated with both LM and SEM observations. Their ecological preferences are derived from the accompanying diatom flora in the different investigated samples and the literature.

KEYWORDS:

• Brachysira
• taxonomy
• morphology
• Europe
• type material
• environmental monitoring

Acknowledgments

Mrs Amelie Jarlman (Lund, Sweden) is thanked for providing recent material from several Swedish rivers. Dr Gabriele Hofmann (Glashütten, Germany) is thanked for sending us the type material of B. liliana and B. neglectissima. Funding for this research was partly provided in the framework of the project DIATOMS (LIST – Luxembourg Institute of Science and Technology). The editor and two anonymous reviewers are thanked for their valuable comments that greatly improved this manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

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Author contributions

Bart Van de Vijver Contribution: LM and SEM analyses of all materials, discussion of results, development, writing, revision and editing of the manuscript.

Tanja M. Schuster Contribution: herbarium research, discussion of the results, revision and editing of the manuscript.

Wolf-Henning Kusber Contribution: advice on taxonomic issues regarding the International Code of Nomenclature for algae, fungi, and plants, discussion of results, revision and editing of the manuscript.

Paul B. Hamilton Contribution: discussion of results, revision and editing of the manuscript.

Carlos E. Wetzel Contribution: discussion of results, revision and editing of the manuscript.

Luc Ector Contribution: provision of literature, discussion of results, revision and editing of the manuscript.