Revision of the Nitzschia sigma complex (Bacillariophyta), a frequent cosmopolitan species in disguise with the description of two new species

ABSTRACT

The original material of four taxa in the Nitzschia sigma complex has been studied and revised based on light and scanning electron microscopy observations. Nitzschia sigma, in this paper lectotypified based on the original Kützing drawing and epitypified using original de Brébisson material from Courseulles (Calvados, France), is a large marine-brackish species with a distinct striation pattern and structure. Several of the studied taxa, originally considered as varieties of N. sigma, showed sufficient morphological differences to be raised to species level or be described as new species, due to nomenclatorial issues. Nitzschia rigidula (Grunow) stat. nov., a freshwater species, originally described as N. sigma var. rigidula from the region around Brussels (Belgium) is the smallest of the new taxa. Analysis of another, former N. sigma-variety, proved to be based on an illegitimate, superfluous Kützing taxon, showed that two independent species were included under the same name, N. sigma var. rigida, that are described in this paper as two new, brackish to freshwater species: Nitzschia neorigida sp. nov. and N. pararigida sp. nov. All species are morphologically characterised and illustrated and their ecological preferences based on the associated diatom flora in the samples, are better defined.

KEYWORDS:

• Morphology
• new species
• Nitzschia
• type material

Acknowledgments

Dr Tanja M. Schuster is thanked for her help with the original Grunow drawings conserved in the Naturhistorisches Museum Wien (Austria) and the permission to use them in this paper. Mr Wolf-Henning Kusber is thanked for his taxonomic advice and his help with the PhycoBank numbers. Mrs Petra Ballings and Mrs Myriam de Haan are thanked for their help with the SEM observations. Two anonymous reviewers and the editor are thanked for their constructive remarks that improved this paper.

Disclosure statement

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

Author contributions

Horst Lange-Bertalot

Contribution: provision of literature, analysis of the observations, discussion of results, writing, revision and editing of the manuscript.

Bart Van de Vijver

Contribution: generation and analyses of LM and SEM materials, discussion of results, development, writing, revision and editing of the manuscript.

Additional information

Funding

Funding for this research was provided by Meise Botanic Garden.