Two new Amphora species from European rivers compared to morphologically similar species of the Amphora copulata complex (Catenulaceae, Bacillariophyceae)

Amphora copulata is a widely reported diatom name in water quality surveys throughout Europe. Following a survey of 1 000 floristic lists from the French part of the Rhine-Meuse basin (2000–2021), seven samples with the highest abundance of this species were selected for detailed examination-based on light (LM) and scanning electron microscopy (SEM) observations. In addition, samples from the Netherlands and Germany with a high abundance of the Amphora copulata species complex were also studied. The specimens previously identified as A. copulata sensu lato could not be assigned to an existing species based on the currently available literature, and proved to belong to two taxa described here as new: Amphora vanderwerffiana sp. nov. and Amphora lucectoreana sp. nov. The two new species are illustrated using both light and electron microscopy and compared to morphologically similar species. As such, type materials of A. eileencoxiae and A. neglectiformis, and recent material from the type locality of A. macedoniensis are also illustrated and discussed.