Typification and morphology of Staurosirella lapponica (Grunow) DMWilliams & Round and Staurosirella pinnata var. intercedens (Grunow) PBHamilton (Staurosiraceae, Bacillariophyta)

For a long time, the identity of Staurosirella lapponica, originally described as Fragilaria lapponica, was unclear as the original type material was never analysed in detail. Analysis of one of the samples used by Grunow to illustrate F. lapponica was investigated here by means of light and scanning electron microscopy. The observations allowed for a better morphological characterization of this species illustrating the ribbon-shaped colonies using bifurcated linking spines, its short striae on the valve face, and a reduced apical pore field. Additionally, a slide in the Cleve & M??ller exsiccatae, bearing the type population of Fragilaria mutabilis var. intercedens, was likewise investigated to determine a possible conspecificity with S. lapponica. Based on our observations, it is clear that both taxa are conspecific, with F. mutabilis var. intercedens being a more recent heterotypic synonym of S. lapponica. Staurosirella lapponica is compared with all other elliptic Staurosirella species. Only S. mutabilis shows some resemblance, but can be differentiated based on a higher stria density and larger apical pore field of the latter.

Automated summary

This study provides a detailed description of Staurosirella lapponica using microscopy and identifies a possible heterotypic synonym. Comparison with other elliptic Staurosirella species shows some similarities only with S. mutabilis.