Gomphonema beaugerianum, , a new Gomphonema species (Bacillariophyta) found in a historic William Smith sample from the Auvergne (France)

A large, unknown Gomphonema taxon belonging to the G. truncatum group was observed in a historic sample collected by William Smith during his 1854 excursion in the Auvergne (France). The unknown species presented sufficient differences with all known taxa in the truncatum-capitatum group to warrant further morphological investigations. Detailed light and scanning electron microscopy investigations in comparison with all published literature revealed that the unknown species had a unique combination of morphological (uniseriate striae, lack of well-develop headpole) and morphometric (large valve width) features. Therefore, the species is described as new: Gomphonema beaugerianum sp. nov. The new species was observed in Lac de Gu & eacute;ry, an oligotrophic, almost circumneutral lake in the Auvergne with a high ecological quality.