Planothidium lacustre (Achnanthidiaceae), first world record outside the type locality

During a study of Iberian benthic diatom flora in disconnected Mediterranean pools, some small populations of Planothidium lacustre were found in Andalusia and Extremadura (Spain). Specifically, in seven pools of temporary rivers in the Guadiana and Tajo basins. Since its discovery in a small pond in Doñana (Andalusia, Spain) in 2013, there have been no new clear records of this species. Our detailed morphological analysis based on optical microscopy and scanning electron microscopy allowed us to show the morphological variability of the taxon. The specimens of P. lacustre are illustrated with microscopic images, and information on their distribution and ecology is provided. Our findings also suggest that P. engelbrechtii could be a species closely related to P. lacustre. They allow a better understanding of this distinctive Iberian taxon and highlight the need to protect Mediterranean temporary pools and ponds, often forgotten habitats.