Taxonomic revision and typification of Gomphonema productum and G. sarcophagus , including the description of two new species from Europe (Gomphonemataceae, Bacillariophyceae)

The observation of an unidentified Gomphonema population in France, which morphologically resembled G. productum, prompted a reinvestigation of the original material associated with this species and the historically similar G. sarcophagus. Analysis of historic collections and protologue data revealed that G. productum had been erroneously lectotypified using material from Belgium that conflicted with Grunow’s original concept of this species. By incorporating Grunow’s authentic original material into the study, alongside detailed light and scanning electron microscopy, we determined that these associated collections actually represent four distinct species. To correct the historical error, a replacement lectotype is designated for G. productum, superseding the previous invalid choice. The superseded Belgian material exhibits clear morphological differences from G. productum sensu Grunow and is formally described here as a novel species, Gomphonema delognei sp. nov. Furthermore, the unidentified French population could not be assigned to any known taxon and is described as Gomphonema pseudoproductum sp. nov. These species can be identified reliably based on valve outline, valve width, stria density, stria structure (uniseriate versus biseriate), and internal areolar architecture.