Taxonomy, systematics, and valve ultrastructure of the Rhopalodiales (Bacillariophyta: Bacillariophyceae) taxa from Swan Lake, Oregon, and a checklist of the group in the USA

Abstract. We describe species of Rhopalodiales found in samples from Swan Lake, Oregon, deposited in the Tempère and Peragallo Collection in the Museum National d'Histoire Naturelle (Paris) and the Academy of Natural Sciences (Philadelphia). A total of eight different taxa have been recognized, and these are detailed with light and, in some cases, scanning electron microscopy. Six of the species are of the genus Epithemia sensu stricto. Within this genus, we describe one species new to science and make two new combinations. Species found in the Swan Lake material belong to the Turgida (one species), Argus (one species), Sorex (two species), and Adnata (two species) groups of Epithemia. Variation is described relative to the course and position of the raphe branches, the structure and organization of the areolae, and the central area. Two species of Rhopalodia sensu stricto are reported, including one newly described species. A checklist of the Epithemia and Rhopalodia species reported from the USA is also presented.