Species of Pleurosigma (Pleurosigmataceae) with lanceolate or slightly sigmoid valve outlines: analysis of type material

Abstract

The type material of seven taxa of Pleurosigma W. Smith were studied, including P. atlanticum Heiden & Kolbe, P. chilense Hustedt & Krasske, P. chilensis var. patagonica Ferrario & Sar, P. indicum Simonsen, P. intermedium W. Smith, P. nubecula W. Smith and P. simonsenii Hasle. All these taxa are mainly characterized by a straight or almost straight valve outline. The fine morphology of the type specimens is studied and compared with similar taxa, and appropriate taxonomic changes are proposed. The material examined included the lectotypes of P. chilense and P. atlanticum, the holotypes of P. indicum and P. simonsenii from the Friedrich Hustedt Center for Diatom Research (BRM, Germany), the isolectotypes of P. intermedium and P. nubecula from the Van Heurck Collection (BR, Belgium), and the holotype of P. chilensis var. patagonica and material of P. simonsenii collected in Argentinian coastal waters from the Herbarium of the División Ficología (LPC, Argentina). Based on light and scanning electron microscope analyses, it was concluded that P. atlanticum, P. chilense, P. indicum, P. intermedium and P. simonsenii are valid species, P. nubecula is a heterotypic synonym of P. intermedium and P. chilensis var. patagonica must be raised to specific rank under the name P. patagonicum (Ferrario & Sar) Sterrenburg & Sar stat. nov. as it differs from P. chilense in the fine morphology of the external central raphe fissures, the valve apex and the areolae near the centre.

Keywords:

• morphology
• Pleurosigma species
• taxonomy
• type material

Acknowledgements

We thank both Bart Van de Vijver and Myriam de Haan from the National Botanic Garden of Belgium who have examined on our behalf the type specimens of Pleurosigma intermedium and P. nubecula. We are also grateful to two anonymous reviewers for their valuable suggestions and comments and to the Associate Editor Eileen Cox for the English revision and the very useful remarks which help us improving the paper. The research was supported by grants from the Consejo Federal Pesquero, from the Universidad Nacional de La Plata 11/N640 and from CONICET PIP0067.