Three new diatoms from North American rivers are described: Staurosira reimeri, Staurosirella elegantula and Staurosirella magna. The features of these diatoms are distinctive, and although they are reported here for the first time, misidentifications and lumping with other taxa in the past are likely. The finding of these three new taxa has two main implications: 1) knowledge of the diversity of araphid diatoms in the Fragilariaceae in North America is still incomplete, and 2) the full set of characters for araphid genera such as Staurosira and Staurosirella is still unknown since the three species described here have novel characters that were unknown or uncommon until the present study. The morphology of the new taxa is shown using light microscopy (LM) and scanning electron microscopy (SEM) and compared with the available literature on this group. S. reimeri is unique within Staurosira because it includes rhomboid, isopolar valves with a narrow linear axial area, rudimentary spines, and apical pore fields reduced to two slits located perpendicularly on the valve mantle edge at the valve apices. S. elegantula and S. magna are unique within Staurosirella due to their large and heavily silicified valves. Both taxa are also shown here to have thick spines with less densely silicified cores, a first report of this feature for Staurosirella. Additionally, S. magna has copulae possessing well developed ligulae that can be folded outwards, a feature that has not been seen in any other published taxa within Staurosirella. Finally, two varieties are transferred to the genus Staurosirella at the species level: S. dubia and S. rhomboides, based on a previous study of these diatoms in North American material done at the LM and SEM levels.
New taxa: Staurosira reimeri Morales, Manoylov et Bahls, Staurosirella elegantula Morales et Manoylov, Staurosirella magna Morales et Manoylov.
New combinations: Staurosirella dubia (A. Grunow) Morales et Manoylov, Staurosirella rhomboides (A. Grunow) Morales et Manoylov.